Infinite Those Guys spawn after 40 seconds1,200f, delay 3~20 seconds90f~600f.
When the base reaches 96% HP:
1 Squire Rel spawns as the boss after 0 seconds0f.
Infinite B.B.Bunnies spawn after 0 seconds0f, delay 1~6 seconds30f~180f.
Infinite Pigges spawn after 40 seconds1,200f, delay 3~8 seconds90f~240f.
3 One Horns spawn after 0 seconds0f, delay 0.07~0.13 seconds2f~4f.
Use anti-Red cats. Summon Apple Cat to stop One Horn's quick attacks, but be prepared to upgrade your wallet as killing the One Horns gives you lots of money.
If you are stuck on this level, you can cheese it by using Pirate Cat along with one meatshield. Use Island Cat and King Dragon Cat to kill the first One Horn that spawns, and since Squire Rel is the boss in this level, you could knockback the One Horns back to the base and then kill the base.
It is even possible only using Bean Cats, Pirate Cat and Sushi Cat and by using the BiohazardCombo. You could also use Jamiera Cat to kill the first One Horn, or to knockback the One Horns if you don't have Pirate Cat.