Challenge room locked at full health
I thought a challenge room would open on full heart and it is as well not a boss challenge room. The door seems to be open when I enter but immediately closes.
Is it because I have picked up IPECAC?
Solution 1:
This room is a boss challenge room, as denoted by the skull inside the swords, to enter it you need one heart or less of red hearts left, meaning that soul hearts do not count.
For more info here's the wiki page