The most traditional or old school Rat that was known for doing this was Ravenous Rats
5/111 Feraligatr (Holo)
Its a large, open space with tables, plenty of plants, and lots of cool Pokmon stuff, including a large, bright neon sign of the movie logo for Pokmon Detective Pikachu with a few glowing Morelull sitting on top
Also, Weavile EX pairs with Cyrus should your opponent wish to switch out the damaged Pokmon
If a creature other than the creature with backup ends up as the target of both the backup ability and the copy, it will end up with two +1/+1 counters and it will gain the non-backup abilities twice
Regardless, players who want to pull this combo off in Historic Brawl can now do so, but milling the opponent will likely require multiple activations