I'd say it's a tossup between Fane's ability and the custom character "Dome of Protection" ability. Fane's extra turn is powerful, but Dome scales REALLY well all game. It's one of if not the strongest armor-heal in the game, competes as one of the strongest overall heals in the game, and then gets reapplied every turn for 5 turns to every party member in range, and it doesn't even hurt your Undead. ALL of the other innate source abilities are shit that you probably won't ever even use.
You CAN time-warp your team mates too.
