Four mana to produce a Zombie for each card discarded is more than serviceable, and eventually you can service your vehicle with a 2/2 Zombie crew member to block with a 5/5 for days or go in swinging if thats whats required
This is a staple of Delirium decks until the end of time
These are all universally playable in a bunch of different decks
Once a novel idea, there are quite a few of these plane-hopping deck-leaders kicking about now
But even there I was always skeptical, since has a shortage of allies who can quest effectively and if you're putting all the questing load on your heroes you're left completely depending on your allies for combat, despite the fact your heroes are probably good at it (And doesn't have the generic readying to let your heroes do both)
While Valki may be based on Loki, the trickster God, hes everyones favorite infamous planeswalker Tibalt in disguise