@Sammichu I have not done this one yet, but I read what you said! Vanquishing a Z-mech can be difficult, let alone 3. Here are some tips I can and will give you, for if you have not already tried them:
- Peashooter can help a lot, because of the Pea Gatling, charge the Pea Gatling, hunt for a Z-mech, and hit him with what you've got!
- I'd say Kernel Corn is also good, because of his damaging abilities and rapid-fire primary weapon.
- Citron would also be decent because of his stun (which stuns Z-mechs for longer), his navel laser can do a lot of damage, his spin dash is good for getting closer to the mech quickly or doing some decent damage to him, and his sprint is the fastest in game (and is unaffected by sprinting nerf) getting you around and to a Z-mech quicker without other enemies slowing you down.
- Rose because of aim bot and her Jinx!
- Chomper as you do a lot of damage when up close, have the option to shoot, burrow to get closer, and grody goop to negate its abilities!
- Snapdragon can help, especially at close range. Swoop slam can be used to get closer! Your abilities can all weaken the mech!
- Acorn and Oak, Acorn has speed and a dash, trap and a fast-firing primary, Oak has high damage, damaging abilities and a lot of health you can tank (especially with hardened upgrade).
Hopefully some of those tips could help you!