You need to get a ranged weapon to defeat it, and then use it while facing the squidbunny. Its meant to be an enemy you avoid entirely rather than just dodge like most others so i assume you just got lucky on your first run
nope there isn't, he's just hard to get so you gotta line him up perfectly with the shot so that it hits him I tried that myself and failed while others have succeeded. But there is a way to get past him without the gun, just keep running when you encounter him and don't be in the same path as him I noticed he can't stun you if you keep moving.