This is only possible with The World card. On very rare occasion, by starting the room when sitting on the plate when you have a terrain passing movement buff (such as Auriun E), you dupe the amount of creeps inside that room, and as a result, 2 keys will appear after you're done with it. If you pick up 1 key only and start another room, then the previous room which you cleared can be restart. However, no key will appear after you clear it the 2nd time. And by the end when you have cleared all rooms, no Lich King skull will appear, no boss fight as you're soft-locked.
This is only possible with The World card. On very rare occasion, by starting the room when sitting on the plate when you have a terrain passing movement buff (such as Auriun E), you dupe the amount of creeps inside that room, and as a result, 2 keys will appear after you're done with it. If you pick up 1 key only and start another room, then the previous room which you cleared can be restart. However, no key will appear after you clear it the 2nd time. And by the end when you have cleared all rooms, no Lich King skull will appear, no boss fight as you're soft-locked.