6 Health as a marker of ‘run health’

I don’t know how best to express this, but TBoI also treats your health as a general indicator of how well your run is doing.

This is most evident in two special rooms: Challenge Rooms and Boss Challenge Rooms

6.1 Challenge Rooms

This kind of room has some treasure inside that, on pickup, will trigger 3 waves of enemies, one after the other. While none of them are particularly dangerous¹⁴, you can’t exit the room until you kill all the waves or teleport away.

These rooms aren’t always open, though. You must have full HP in order to open them. Well, kind of.

For example, consider having a single red heart, two empty heart containers and three demon hearts: 💖💔💔🖤🖤🖤 This is enough to open the Challenge Room, since you have a total of 4 hearts and 3 heart containers.

In other words, Challenge rooms require that you be «at full health» or equivalent in order to tackle them.

6.2 Boss Challenge Rooms

Like regular Challenge Rooms, but this tends to have better rewards, but instead of three waves of enemies, you get to fight two rounds of bosses, one after another¹⁵.

Like regular Challenge Rooms, these are open only on a specific circumstance.

Again, this takes into account your red hearts, not your heart containers. And yes, you can have zero heart containers and it’s often a good strategy to have this little HP!

Observant readers will note that, unlike regular Challenge Rooms, these require that you be «near death» or equivalent in order to tackle them.

14. compared to the floor’s power level, that is.↩︎

15. Observant players will note that it’s not necessarily two bosses, but two rounds. You might have the bad luck of having the pink variant of Monstro, which always spawns in pairs and sometimes in fours.↩︎