First you NEED to have 100% treasures on chapters 1, 2, and 3. 1 important fact is at level 20 with 300% treasures, can survive a hit from Bun Bun.
Lineup: Macho, Wall, Boogie (probably mandatory, though you need to test this), Dragon. In fact, you don’t even need Valkyrie if you have 300% treasures. Maybe bring a cpu.
1. Lure Roo and spam wall and dragon. If you can’t, consider using a worker level up combo. While killing it, upgrade your worker cat.
2. One you have killed roo, spam only Macho and Wall, and dragon. If done correctly, you should have a stack of dragons by the time you are halfway to the base. Don’t spam boogie due to cat limit.
3. Once you have gotten to the base, cat limit will wear off, and spam everything. Most importantly, spam Macho and wall in such a way that you send a wall when Macho is half way through cool down, and vice versa.
4. When bun bun comes out, don’t stop spamming everything. Turn your cpu on.
5. With this strat, you should win. If not, force close battle cats (if on iOS, double press home, and swipe up on BC).