@Elwyn
Leech heals you for 5% of your max HP, every 'tick'. This means that you can instantly ignore (5%maxHP) from any physical damage you take.
So as an example, my Leech/GlassCannon mage has 12 Constitution and 1032 HP at level 21. That means he ignores 52 damage from every physical attack he takes. When I put an elemental shield on him, he actually GAINS HEALTH from people attacking him with swords, because the shield absorbs damage but he still bleeds.
Note that if I hadn't given him Glass Cannon, he would be healing for twice as much each time.
However because I >did< give him Glass Cannon, he gets +16 AP per turn. And because Glass Cannon lets you focus less on Speed, I was able to pump his Constitution up higher than my warriors (who don't have glass Cannon). As a result, my Madora only has 20% more hp than him, but she has WAY fewer AP per turn.
