I was playing on Going Rogue, Permadeath. I was on the 2nd Floor, with a Wyrmling blocking off part of the Monster Zoo, when I placed three Runes of Exploding well inside the zoo. I was Level 7 at the time. I level up, and I believe other monsters died the same turn I leveled. As a result, I ended up leveling up 3 times and when it ended I was Level 10 (and assigned three skill points). I don't believe it is anywhere near possible to get that much experience in one shot from a few runes going off on Going Rogue, Floor 2.