Wave 2 CBT Rough Guide:
Now that there is clout associated with completing CBT due to the website's badges, I am going to keep writing these as (hopefully) there will be at least some demand to continuing to play the mission. Personally, as I have said, I find CBT extremely fun, and would be happy to play it again and discover new strategies which might work to complete the various waves, or strategies which might work with fewer players. That being said, I am going to continue writing these guides for 10 man teams attempting to play to win, not to try silly shit.
Starting with wave 2, assuming there was perfect credit collection on wave 1, you will have 600 credits. Now that the door has opened into getting basic upgrades, many more things become viable, and I won't be able to speak on every single possible strategy that a team could use. I will, however, still attempt to discuss the strategies I believe would probably be most commonly employed and the strategies I believe are the most effective. I also assume that if you're reading this, you've probably gotten to wave 2 or at least read my wave 1 guide, so I'm going to guess you are competent enough to know not to do things like shoot the uber medics early, and I won't repeat something so basic.
The first group of robots that spawns in wave 2 is two groups of 12 heavies. These always spawn out of the left (open sky) spawn. Any class with good AOE can deal with these rather well, although ones which can deal AOE without needing a sightline will be superior. Having said that, a demo should not use his stickies to deal with the heavies, as others classes or weapons can attack them and the stickies should be saved for later. Demo can, however, spam pipes (preferably loose cannonballs) over the wooden structure on the left to hit the groups of heavies. Gas pyro can be used here, although because the threats at the start of the wave do so much damage, it can be very difficult to get close to do damage to recharge the gas to throw it on the second group of heavies. Explosive headshot sniper is also an option, but you need both a sightline and multiple shots to kill the heavies. Soldier actually starts being good on this wave with the ability to upgrade reload speed and rocket specialist. Will go into more detail on upgrades and loadouts later, but rocket specialist beggar's with a tick of reload speed is great AOE, especially if you use a banner. Medic can use projectile shield to block shots from these heavies in order for classes like soldier, pyro and sniper to more effective damage the heavies, but if there is only one medic, he should save his projectile shield. Heavies are slow, and if you kill the first group with something like gas, by the time the second group of heavies comes around the right side of the rock, they will almost certainly be stacked with the next threats and receive splash damage from attacks on them.
10 seconds after the heavies all spawn, a stream of 12 super FaN scouts will begin spawning, one every six seconds. These should be body blocked and kept in front of the choke with heavies, sentries, and knockback classes such as the pyro. Despite the fact that the brass beast does 60% more damage than the natascha, using natascha is superior as slowing down the scouts keeps them in the range of the other damage dealers on your team longer, such as sentries, other heavies running brass beast, rocket specialist soldiers, and more. If a single scout does get past, a soldier with rocket specialist and +reload beggar's can jump and hunt them down. The bomb can be left alone so long as nothing else gets through the hold, but if a second scout after that ever gets past, people should start falling back. Hopefully this will be one of the later scouts, so the NEXT offensive threat to speak on is gone or hindered.
16 seconds after the heavies spawn, the first of three squads will spawn: Giant crits burst fire demos with 8 uber medics each. Fortunately, the second and third squads will not spawn until the first is killed, but the second squad will spawn as soon as the first dies, and the third will spawn 25 seconds after the second group spawns, irregardless if they die or not. THIS is what the demo should save his stickies for. 14 damage upgraded kritzkrieg'd scottish resistance stickies will one-shot the demo and any meds near him. This is by far the most effective way of dealing with these demos. The amount of spam can only be dealt with by a medic's projectile shield, but as this is a burst fire demo, the pattern he with which he spews pills can lob over the medic's shield and destroy the hold next to instantly, as this wave does not have enough money to buy resistances. The most consistent strategy here, I believe, is two scottish resistance demos who both prepare traps before the round starts. The first demo one shots the first demo's squad, which will instantly spawn the second squad, the second demo destroys the second squad, and then you have 25 seconds for the medic to kritz one of the demo's to lay another trap. The demo which is not kritz'd should also lay a trap of his own to clean up in case the the crit trap doesn't one shot the third demo. Fighting these demos any other way can easily spiral into an entire team wipe, which will necessitate use of buybacks, which is unwanted during such an early wave. The medic should activate his shield when the first giant demo spawns, as he will start spamming, and you don't want to lose the choke hold on this wave. For trap locations, all of the sticky piles should be laid just around the right corner of the rock, where you can first see the robots. This way you kill the demoman where you can see them, so you can be 100% sure your trap is going to land, but it will minimize the amount of time the giant demo has a sightline to the hold and might start lobbing pipes at the rest of your team. Additionally, the demo squads can spawn in either the left or right wooden spawns, but they will always go around the right side of the rock, so putting your trap in this location will account for both spawns.
If you can't get 2 demos, or nobody wants to play him at all, explosive headshot sniper and gas passer pyro are must-haves, because nobody else can deal with medics on this wave unless they have kritz (but using canteens this early is not worth it and a kritzkrieg charge isn't long enough for a soldier to kill the medics in all three groups). With proper projectile shield use, it may be possible to kill the demoman with kritz brass beasts before they can get pipes to ricochet and destroy the entire base, but really - just use demoman. Scottish resistance is simply absurdly powerful.
Next, support bots - first to mention, although they are technically part of the actual wave and not support, 40 seconds after the heavy dies, 3 groups of 8 crossbow medics will spawn, 2 seconds apart from eachother. They're practically pointless and can be killed by anyone, despite the fact that they do non-negligible damage and healing, their tiny health pools make them mostly a non-threat. Gas passer or explosive headshot can obliterate them with very little effort. The next support bots to mention are the spies. 45 seconds into the wave, and every 35 seconds after that, 4 spy bots will spawn. They aren't too much of a threat, especially considering you get a notification when they spawn, but I have been backstabbed while focusing too hard on my trap usage more times than I would like to admit. Keep in mind spybots spawn behind you in the actual map as opposed to the normal spawn areas all other robots come from. The final support bots on wave 2 are sydney sleeper snipers. At 60 seconds into the wave, and every 40 seconds after that, 3 sydney snipers will spawn. I have literally never even noticed these, as they die so quickly to the heavies and other combat classes. For the final support to mention, wave 2 once again has an absence of sentry busters. This means running multiple engies to enhance the sentry-walling capabilities of your team against the FaN scouts is perfectly viable, but once again, no free ubersaws.
Moving onto team comp, engineers are invaluable. I didn't touch on the FaN scouts as much as I spoke on the giant demos earlier, but a super scout which can knock bodyblocking players out of the way is a huge threat in terms of getting past players and running the bomb to the hatch. Sentries, of course, cannot be knocked back. I would recommend at least 2 engies, one to put a bodyblocking sentry on each base-side corner of the choke. 2 demos is also incredibly powerful as mentioned, and will make the encounters with the giant demos much, much easier. Gas passer pyro and explosive headshot sniper are both viable options for crowd control against small bots and killing uber medics if the demo messes up, but personally I believe pyro to be superior on this wave for his ease of use and ability to airblast in case of emergency bomb hole defense. On the other hand, sniper's explosive headshot isn't on any kind of cooldown like the gas passer is, and he is more effective against the giant demos. A medic is all but necessary, because playing without a shield and kritz - two things necessary for some of the most effective strategies in the wave - and instead using neither is a recipe for disaster. Nothing will be able to kill the demo quickly, and his pipes with instantly tear through the team's entire base. As there are zero tanks on this wave and the uber medics come in fairly easy to deal with groups, heavy is extremely effective as both a utility with natascha against the FaN scouts and dealing the highest DPS in the game at this point with brass beast. Heavies should be sticking with the engineers, helping them body block and killing the FaN scouts. A scout is also necessary at this point in the game, as you want 100% credit collection on this wave to make the future ones as easy as possible. In my opinion, if you lose credits on wave 2, you should throw the game, as you only get 250 credits on this entire wave, so the 100 credit bonus is incredibly important. If you complete the wave with missing credits, you would have to repeat wave 1 as well as wave 2 in order to get those credits back, and early waves in CBT are very cash-dry. Soldier is viable on this wave, but I still think he is outperformed by other classes. Buff banner is always a good thing, and battalion's backup can actually make your teammates capable of tanking a couple of the giant demos' crit pills. If you have more than 3 damage classes (including you), switching to buff banner soldier will ultimately be a damage increase. As for spy, he's still a meme, and I honestly don't think there's a single wave where he is actually viable. Certainly not any waves where he is meta. Although who knows, maybe I'll be the next clown to get quoted for calling something in CBT bad or impossible only for spy to be later proven the most powerful class in the game somehow.
Next, loadouts, upgrades, and any other playstyle tips I think of while writing this section. Now that we have credits on this wave, there are tons of options as to what you could upgrade, and as mentioned earlier, I can't cover everything, but I will say what you should gravitate towards. Starting with scout, keep using Bonk!, there's nothing else available on this wave that's going to let you run into a battlefield filled with groups of heavies and giant crit burst demomen. Considering you're using Bonk!, resistances aren't as necessary, so prioritize movement speed first to make your Bonk! runs faster and more effective. Use fan o'war if you want to and can, but you should really be focusing on just credits here. Next, soldier. I mentioned before that he seems suboptimal, but he's certainly not bad. Your upgrade and loadout on this wave should always be beggar's, one tick of rocket spec, one tick of reload speed, as mentioned earlier, and buff banner or battalion's (although with competent medics or demomen, battalion's shouldn't be necessary and boosting the damage of your heavies and other damage dealers will be better). Don't use conch, the movement speed won't do much and the lifesteal, as with wave 1, won't outheal anything on this wave. If you get hit by crit pill spam, or you're in the line of fire of a dozen heavies, conch healing is not going to save you, and if you aren't in either of those scenarios, you're probably not taking significant enough damage for conch to be useful. Trust the medic to do his job. For pyro, don't use the phlog, you're not going to be able to go in and use it anyways, and airblast is the best use for your primary. Use either stock flamethrower for maximum airblast spam or dragon's fury, as the extended reach and higher single target damage will be better for charging your gas passer. Speaking of, use the gas passer. It's not quite broken here, as it is difficult to get in and charge when you have next to no resistances, but it kills groups of robots just fine even if you can't charge it faster. With the rest of your credits, you probably won't be able to buy anything relevant, so get a tick of crit res or something. For demoman, use the tried and true loose cannon + scottish res combo. Loose cannon is extremely good at spamming from ideal distance for high dps, damaging enemies not actually in your sightline, and doing knockback to bomb cappers or other threats. Scottish resistance one shots the giant demos and their uber squads, it's a wave-carrying weapon. For upgrades, I always put 500 credits into a tick of +20% scottish res damage to secure the one shot, but I'm not entirely sure if that damage is necessary or not. If it isn't (big if), then reload speed will be your best bet. For heavy, you can either buy some knockback rage as a save option for the bomb and general scout position control, or buy some firing speed for higher damage. As mentioned earlier, the first heavy should use natascha, and heavies after that should use brass beast. Your job is scouts, or demos if something goes wrong dealing with them. For engineers, building health and dispenser range are both excellent options, but building health + building canteens is probably the best bet. Keep using stock wrench with wrangler for maximum tanking. For medic, there should ALWAYS be at least one kritzkrieg medic to assist demos, but medics after that can use either kritz or quick fix for better shielding. Vaccinator is fine, but quick fix is better as vacc only protects yourself and your current pocket, while shield will protect the whole team, and because most of your healing will be overhealing, vacc generates shields much slower. Vacc's crit res against the giant demos hopefully won't be needed if the team's demos can kill them. Obviously, having spent most of this guide talking about it, projectile shield is the upgrade you're going to want to get. You can either stack it or get 1 proj shield and 1 healing upgrade. Canteen specialist and uber upgrades should not be used on this wave under any circumstances. Sniper should use heatmaker, it's the best sniper in the game by far and a weapon which competes with the scottish resistance in terms of performance in normal MvM. Unfortunately this map's tight choke makes sniper hard to use, but he's far from useless. Secondary can be jarate, although that becomes redundant with other sources of mini crits such as a buff soldier or fan o'war, or cozy camper. Buy one tick of explosive headshot and one tick of reload speed. Use focus as much as possible. Spy is a meme, don't play him.
The general strategy is pretty obvious from what I've said already, so I'll just mention a few more things: If you have a pyro and the bots go far left, they will go past a pit which the pyro can airblast them into (or other kb classes can do the same). This can be an easy ticket to kill a super scout which gets past or a giant demo which has broken through defenses and reset the bomb, although catching up to these before they pass the pit as a pyro with gas passer equipped can be difficult. Other than that, fallback strategies are the same as they were for wave 1, although falling back at all in this wave can be prevented more consistently and also is more likely to result in your loss if it does happen, so the easiest way is to simply hold the choke for the entire wave.
I honestly thought this guide would've been shorter than the previous one, because the bots on this wave are simpler and I didn't have to explain basic shit like not shooting uber medics, but I'm coming up on 17000 characters. I'm gonna have to make smart cutting decisions to fit this in 6 posts. (i failed lole). Once again, if you have any feedback, feel free to tell me. CBT has captured my autism and I like to talk about it, if you couldn't tell.
For a final note, I believe an optimal team comp which could complete the wave with 6 people is as follows:
2 demos, loose cannon + scottish res, +20% damage on scottish res upgraded
1 heavy, natascha, knockback rage
1 medic, kritzkrieg, projectile shield + healing mastery
1 engineer, wrangler, wrench, building health + building canteens
1 scout, bonk!, max movement speed