The Red Cat Gambit is the final stage in Coup de Chat.
Battleground
This level has three bosses, that's all there is. As soon as the battle begins, Othom will be spawned as the first. Later, M. Ost will appear as the second. Relic Bun-Bun appears as the third.
Strategy
Simple stage, Rodeo with anti-relic talent, meatshields and Slapstick is all you need.
Alternatively, it is possible to use units such as Sniper the Heavy, Kubiluga or Ultralan to stunluck the enemies close to the base while some LD Ubers slowly destroy it.
Strategy 1 (Cheese, No gacha)
Lineup: Gross Cat, Crazed Gross Cat, Creepmallow cat, Cat O'Lantern (Freeze Up sm+m) Healer CC Little Leauger Cat
(None of the cat's levels matter)
Breakerblast Cannon
Let Othom hit the base, and send out Healer to permafreeze it. Stack little leaugers, and time breakerblast so that it doesn't interrupt Healer's attack. That's it.
Video link to strategy[1]