As far as play-ability goes, Trevenant is not terrible, but its second attack is a bit below average. Being able to force Confusion on an opponent is pretty good, however.
The second attack is Sleepy Ball, which requires 1 Fairy Energy and 2 Colorless Energy. It deals 60 base damage, but also puts the opponent’s Active Pokemon to sleep. This is very solid, even if the opponent’s Pokemon wakes up in between turns, since this attack will always hit.
While both are good cards for collectors to have, the Slurpuff definitely has the game-play advantage for being a very solid way to slow down an opponent’s game plan. The Trevenant is a bit under-powered for today’s EX dominated format.