Snache, Those Guys, Croco and Kroxo appear as peons.
Calamary serves as the boss, spawning alongside several peons and two Ginger Snaches. More Ginger Snaches are spawned eventually.
After some time, Helmut Krabbes appear as added support.
For Chapters 1 & 2: To deal with Helmut Krabbe, stall him and hit him with long-ranged attackers. Save your Cat Cannon for when his Lethal Strike ability activates.
For Chapter 3: Calamary on its own isn't very hard, but 2 flops things around. To deal with it, use strong cats like Crazed Bahamut and Holy Valkyrie. If you have Castaway Cat, use him. Most cats that outrange Calamary will also be of use.