To put it bluntly, Screaming Nemesis is a very good MTG card, although they are somewhat situational
At the beginning of combat on your turn, another target creature you control gains haste and gets +X/+X until end of turn, where X is that creature's power
However, Gengar's popularity in Japan is significant as well, as evidenced by this Mega Dream ex's price tag
Usually its given three sealed booster for each contestor, the end goal being the construction of a forty-card deck
If youre close to the end of the game, use Diabolic Intent to search for your win condition
Its a powerful effect, and without it, many decks would be at the mercy of decks designed to stall or control the game