Comeback Kid is fine. Doesn't need a fix.
Fixing Leech is simple - only heal when you ENTER a pool of blood, and change it so that it doesn't consume the pool. This prevents the character from healing one billion times while getting hit / being hit with bloodletting.
Sneak is also easy - make the enemies "look around" when they can't find any of your party members. Literally just walk toward your last known location, and rotate their facing a couple times.
Invis is fine as is, imo. It's not spammable unless your entire party is mages, and even then it still has a significant AP cost.
Alternately, you can add detection based on hearing. If an enemy walks too close to you while you're stealthed/invisible then it removes your stealth/invisibility. Enemies all already have a 'hearing range' stat, same as the player characters.
Last edited by dirigible; 25/07/14 08:45 PM.