Play dretch through stealth when alone or in a group with anything less than a mara. When breaking out of hiding, it becomes about killing them as fast as possible, since humans can grossly outmaneuver dretches (they could in 1.1 too really, but dretches were smaller and harder to hit while moving quickly in that). Don't retreat with dretch if you get weak. That just assumes that you leaving there is going to save your team one feed when in reality it might mean your fuckface teammates going and getting killed more easily, possibly resulting in even more feeds. Waste of time anyways, dretches actually aren't worth shit relatively, the times I scrimmed in this version made it pretty apparent that you could afford to be reckless pretty often with them even in more formal play.
Don't bother fighting with lisk until you get very good at wallwalking and decent at aiming. You'll also need solid reaction time. However, if you're a low HP dretch with 1 evo and there are no enemies around, evo to lisk and you'll heal faster, although this only really works out well if you think you can follow up, or if your team is S1 or you're too far from base at higher stages.
Mara is probably the most beneficial class to learn in the game, because its aim/movement correlation will improve the aim of your dretch, lisk, and human, the reason being that aiming with the mara is largely about learning to control your aim in every way while changing your movement in all aspects, all of this at once. Sometimes you have to do a huge circle with mara if they circle around you, sometimes you have to just stay locked on steady in front of you, etc...Don't use zap against enemies unless you feel like it's actually going to do something and the delay won't hurt you; it does have a long fkn range, so work with that I guess. Also, its mobility is overrated, the only reason to even learn how to jump with mara is to get away, and to be honest, it floats so badly now that you're probably fucked anyways if you get that weak. I can rarely get away with mara easily if I'm chased by someone who can move quickly, and I know how to move with mara pretty well. Also, if you try to use mara against groups, you're either going to just get raped, or your team will consist of dragoons who have to use pounce to do any damage, which will probably fuck you up badly since you'll either get pounced or your potential targets will get pushed away, and distance between yourself an enemy is more deadly to the mara than any other class, except dretch and lisk (but that's more of an initiation thing for those two classes, while for mara, you'll get outmaneuvered).
Dragoon is absolutely necessary to learn, despite it being the most unique class. I'd bet on 3 S2 humans with shotties over 8 maras in a fight between the two groups, all with decent skill on their own parts. But 2 good goons and maybe a dretch or something could take them. Learn to pounce spam first, boring as shit as it might be; there's no point in even trying to learn the fucked up chomp of GPP until you know how to stay close to your enemy and counter their general movements. If they dodge a lot, you'll have to be even faster. Understand that there is no delay between when you chomp and when your pounces can deal damage (in that order). If you miss your chomp, you can pounce as fast as possible afterwords and it will hit them, but to be honest, you're not going to effectively chomp anyone who spams dodge, because by the time you catch up with a pounce, you either knocked them back out of chomp range or you landed in front of them and they dodged again. But keep in mind that if they dodge as they get hit by a pounce they can actually go well out of anything less than a strong pounce's range, essentially fucking you over completely in the fight. Prevalent message: The goon is the only real "all around" class in the game, and it's a fkn shitty one.
Rant is my weakest class, but it's the easiest one conceptually: if the walls are tight, charge the enemies into them, and they will probably die. If they don't, slash them. It's only any good for base defense and directly attacking their base though.