pokemon evolution mewtwo card - Mega - Ascended Heroes Psychic / 130 / Basic Attack 1 Pokemon - Mewtwo-EX (103/108) -

Not Effective : Your moves will have little effect on your target

How to solve the quandary, besides not making UB sets that don't have fleshed-out fantasy worlds

It really depends on the deck and the meta

Take a look at stuff like Tuktuk the Explorer, Godo, Bandit Warlord, or Pia and Kiran Nalaar for some examples of such legendary creatures

Cast Through Time, an Enchantment from Rise of the Eldrazi that grants all your instants and sorceries Rebound, and Narset Transcendent, a Dragons of Tarkir Planeswalker with a -2 ability granting your next instant or sorcery spell Rebound

More info on foil types and versions LINK