All these possible exploits are reported by a friend.
First, try to lower the cost of Spell Leech. The friend claimed to be able to lower it to 3 mana. Then, find a Air Elemental and fight. The AE will try to cast Titan's Breath. So, use SL and if successful, 40 mana is gained. The problem is that the AE is likely to continuously try to cast TB. The friend claimed in one battle, he SL-ed 8 times in a row and the AE came over for melee fight for 2 rounds and got SL-ed twice again as he was able to get away from the AE. hence, almost 400 mana was gained in a single fight. He felt that was way too imbalanced.
Glitches: 1. when infected enemies was shrinked, all other enemies kept the same size. however the other enemies did get the shrink effect. 2. when shrinked, the juggernaut attack was zeroed.