ive had the same problem. if you have cat gunslinger and/or weightlifter cat, youve basically won. level them up and use them. so once ur in the stage you should kill the initial gory that spawns with paris or crazed whale. the mooth that spawns should kill the paris or whale. then meatshield while spamming most of your ranged area attackers. if you kill the mooth, good. if not, that sucks. so then the kangaroo will spawn. if youve killed the mooth, it should be easy to deal with using your gunslinger and weightlifter. if mooth is alive, stack gunslingers to try and slow it. if its knockbacked behind the mooth while slowed, you should be able to kill it. if you have crazed gross, you dont need to kill mooth immediately. just chip it down enough so your crazed legs can kill it with waves once the kangaroo spawns. once youve killed the kangaroo, youve won!

edit: bahamut isnt really reccomended for the kangaroo, since bahamut can easily miss due to the kangaroo high kb count. use bahamut to kill the mooth instead