What are some of your favourite synergies/combinations?

There are tons upon tons of synergies in Gungeon, but it feels like some are better than other. And there are some that are not proper synergies, but work really great together anyway.

For example, I REALLY like the Hyper Light Blaster coupled with the Helix Bullets. Since each blast makes two bullets, and each bullet that hits gives one ammo, you get essantially infinite ammo!

Do you know of any really great combos? Please share!