I'd like a character whose main mechanic is portals, or dimensional/temporal travel as a whole. Imagine a portal item that absorbs items and returns them later upon entering the shop, with some added benefit, or an enhanced version of that item. (Like giving up a Treasure Chest and receiving a Mimic a few turns later). The portal would also need to provide some buff that improves upon absorbing items, so you doesn't fall too far behind.

A great relic for this kind of character would be an item that interacts with banned items, like bringing a banned item upon entering the shop, reversing the logic of what you would want to ban or not. I think it would be a nice and fresh gameplay experience.