This is the easiest (and most full proof from my POV) but probably most time consuming way to kill it, a few already mentioned above and is applicable for all levels, I'd probably just go into more details.
1. Get 50 wraiths/summons. Advice would be to get Lings and Zigreds. Why Lings and Zigreds? They die quick, the aim is to use up the Tuver's (or every other custodians) ability to heal off a killed opponent. To those who don't have room in backpack, make room. Grey, green and blue Lings = 21 summons and only 3 backpack space.
2. After the 50 are dead, use stronger summons. Those (unused) zombies in backpack does the trick. The point here is to let your wraiths/summons kill Tuver, not you. Also remember to use summons whose level is not higher than you.
3. As for belt, giant, 2-3 slots of vamps, 1-2 slots of life and rest red heal scrolls.
4. Try to skip/run down timer for your hit, only hit on every 3rd turn.
5. For mages, stay in Magic Stance, as you don't block or dodge. For non mages, use vamp and heal scrolls whenever possible. Always try to maintain HP above 50% just for the sake of "safety first".
I ended up using (no buffs) 1 life pot and a coupla vamps, used 40ish zombies and some summon decks.
Some may go physical and try to "stun kill" Tuver, but just imagine you stun it, then in the following few hits u crit a few times. 3x crit (in a combo) is... deadly.
Always stay safe and use protection (most fool-proof method)