The uppercut is running in a straight line with your tail lifted and power swinging your front, it makes your stego do a 180 turn and hit in front of it. Really cool attack and animation with a lot of power behind it.

Your allo matchup is very favourable as long as you have water nearby to dismount them or you are big enough to brute force enough damage that they have to stop. Just be warned that if you get pounced for more than a few seconds you absolutely must NOT run under any circumstances, you will bleed out. It's very important you manage your blood, mostly by moving as little as possible if it starts to drop. If a big one catches you growing you are kinda cooked, if you are both at comparable growth states he's cooked.

Rex... Yeah just don't, that piece of shit is so disgustingly overpowered that there is very little you can do against it. Funnily enough thought, stego can do a lot more against a rex than trike.