Red chest mechanics.

- 5% teleport to the Devil room / Angel room
- 7.25% it spawns a soul heart
- 7.25% it spawns two soul hearts
- 10% for a Guppy Item (see details below)
- 10.88% it spawns 3 blue flies
- 13.6% it spawns two super troll bombs
- 14.51% it spawns two troll bombs
- 14.51% it spawns two pills
- 17% it spawns two spiders


Details.
=== Will spawn a Guppy Item with a 10% chance. ===
If Guppy's tail isn't unlocked, 25% chance it will be either the Dead Cat, Guppy's tail, Guppy's head or Guppy's paw.
If Guppy's tail is unlocked, 20% chance it will be either the Dead Cat, Guppy's head or Guppy's paw and 40% chance it's Guppy's tail.
Yeah, that's obviously a bug.

Source of the aformentioned bug, where f1 is the item:
f1 = [81, 134, 133, 145]; // Guppy's tail is 134
if (_root.SecretUnlocked[79]) {
   f1.push(134); // Pushing another Guppy's tail in the random pool.
}
f1 = f1[random(f1.length)];

=== About the teleportation ===
Oh you know the mechanics. 1/15 chance to go to the I AM ERROR room.