All in all, this makes Warp a potential hit of a mechanic, right
When the last is removed, they may cast this card without paying its mana cost
You have to pay a truck load of mana (7, 10, 13, 16, etc.) to have this even do anything, and the effect itself is of course completely unreliable
National Champion Ali Aintrazis Top 16 deck from Grand Prix: Charleston: "Ali Aintrazis Five-Color Door" Creatures (6) 1 Angel of Serenity 4 Thragtusk 1 Griselbrand Planeswalkers (4) 1 Garruk, Primal Hunter 1 Nicol Bolas, Planeswalker 1 Tamiyo, the Moon Sage 1 Vraska the Unseen Spells (23) 2 Abrupt Decay 3 Sphinx's Revelation 2 Rakdos's Return 2 Ranger's Path 3 Lingering Souls 3 Supreme Verdict 4 Farseek 1 Oblivion Ring 1 Door to Nothingness 2 Chromatic Lantern Angel of Serenity, Griselbrand, and Garruk, Primal Hunter in the same deck