So, I bought a gold Mystery Snail today, and once I put it in Sir Lefty's tank, he wouldn't stop attacking it. So I had to switch him into Annabeard's Sterilite, and switch Annabeard into his old tank. I decided to divide the tank I put her in, so now I have space for yet another Betta.
Funny how things work out, right? At least I didn't have to downgrade Sir Lefty. He went into another 5 gallon container, which is nice. He seems a bit miffed, though. He's like "HUMPH. No more filter current to play in!" Well, that's what you get for being an Attack Fish!