So netting a +1 ability on a Planeswalker that Arenas you is certainly something you'll find useful
The ability to play on other turns really becomes incredible when you can ramp, draw cards, and grow a huge trampling threat at instant-speed
Regardless, the pairing makes for a great aesthetic, with the smaller, more innocent Mew being dwarfed by the more powerful Mewtwo
Im sure there will be some spots where it is correct to pick it up, but I would want to get it late in the booster, ideally on the wheel
Although your opponent gets to put something out too, youre usually dropping an Emrakul or an Omniscience that ends the game before they can use their new toy
Some of that values tied to good colorless staples like Skullclamp and Lightning Greaves, too