Bangboo for Godyabi team

Hello, fellow Miyabi enjoyers.

I have Miyabi M4 (for now) and I was wondering what Bangboo to pair with her. I know everyone has asked this before but I'm still deciding.

I have R1 Sharkboo, R2 Knightboo (didn't do the event in time), R3 Penguinboo and I haven't pulled for Gulliver yet.

My team is Miyabi, Lycaon, Soukaku. Bangboo's aren't really a dealbreaker eitherway but I'd like to optimise whatever I'm able to. Also, could someone be so kind as to explain what Gulliver actually does? I've read everywhere and I'm still lost.