Here's a fun little bug, based around Custom Equipment that tinker with stats and go to level entrances under certain conditions.
As a full example, let's say the player has a Custom Armor with the following script:
Each defend "Defend"
Go to "End"
Label "Defend"
If ...
Wait until var _HP < 1
Set var _HP = 1
Go to level entrance "Hospital: Once West: Waking up"
If End
Label "End"
Now, right-clicking on an enemy that you cannot kill in one hit will start causing problems. You will get the Expected Damage of Death, even if you would easily survive the fight and not trigger the Level Entrance move. On top of this, various effects may occur immediately after this, including any movement causing the previous movement to replay, or the Go to Level Entrance command being run, or similar. Undoing from this can also cause problems, like completely removing the last enemy you killed in such a way that restarting the room doesn't cause it to reappear.
Whilst the "
Go to Level Entrance"
command is obviously the major trigger for this, it's not the only problem. If you remove the command, for example, and leave this piece of equipment as something that keeps your HP at a minimum of 1, then the Expected Damage for all fights where you take any damage at all is Death, even if you would come nowhere near the amount of HP needed to activate the condition. (Attacking a Roach when you have 40 ATK and 10000 HP, as an example, would still show an Expected Damage of Death.)
I realise this is a rather unorthodox use of custom equipment, but having it work as you might expect from the code could allow for some very interesting behaviour, and at the very least, the bugs resulting from this need to be closed up somehow.