Blood Clot Boy. I'm happy to brag
I got that one before
Brimstone. And Maggot. I haven't even gotten Maggot yet.
Dark Hospital really isn't all that difficult if you know what you're up against. I suggest heavy usage of Captain Viridian if you have him, as there's a lot of levels he makes much easier, like Dust Bunnies (where you can esentially flip to the celieng and run to the end with minimal ulcer-dodging), and Agent Orange.
There's a few troubling levels in there squished in with the easy ones. *Shakes fist at Grey Matter* But, overall, it's probably the easiest Iron Boy run that actually requires some significant planning to get through.