To tackle Craaazy difficulty you'll need a team of Players who know what they are doing, know how to use their characters and who preferably have them buffed with some upgrades. That seems like common sense but bear in mind a lot of children play the game so you never know who you'll be thrown in with and what they can do if you don't form your own Group before hand.
You'll definitely want at least one Scientist who knows how to play him, I'd recommend the Chemist or the Computer Scientist. Out of all the Scientists I personally prefer those two because the Chemist has the widest damage spread (and the shortest range) and the Computer Scientist has his Crunch Time Legendary ability.
For the rest of the team it can vary but I'd personally have Toxic Brainz for his ability to Toxicate and his Toxic Overload Legendary ability which is pretty easy to charge. Combine him with a Scientist in back linked with a Heal Beam and any Boss Battle thrown at you gets easier.
For All Stars I prefer the Motocross Star with his ability to deny Plants their Soecial Abilities by mucking them up, but the Goalie is a good second with his freezing ability.
For Foot Soldiers I prefer General Supremo with his Infinite Ammo; if you have good burst control you don't lose any time with reloading.
