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?
Best Answer
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.
The doors are tied to your health. The door will only be open if you have full health. However, the temporary HP boosts (blue hearts) can serve as a equivalent of the missing red hearts.
For example: If you're missing one red heart but have one blue heart the door will open. But if you're missing two red hearts and only have one blue heart the door will still be locked.
I saw this from another forum. The lag is akin to "walk on ice", so you will still move to a direction a few milliseconds after having released the directional button.
There is one setting in the graphic options that will solve that. Set the details to "Low". That is it, no more lag. It is probably related to flash overall poor performances. It changes the game from unplayable to "omg its soooo good".
Best Answer
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