Rainbow mode with the bullet is insane...

Since the bullet doesn’t need any guns, you can just load up on crazy passives. I got lucky and got lead god due to picking up clone from a chest (much easier to get it than in regular mode) and am currently sitting at 10 heart containers and 7 armor going into bullet hell after my first death and re-cloning. If you haven’t tried the mode out, I encourage you to take a shot at it. It reminds me of BoI: Afterbirth’s greed mode.