You know, Slivers are missing something...

needs moar planeswalker

Walker Sliver{WUBRG}{Loyalty: 4}
Planeswalker - Sliver Hive
+1 - Put a 1/1 Sliver Spawn token onto the Battlefield.
-2 - Target Creature becomes a Sliver until end of turn.
-7 - Until end of turn, all Slivers get +X/+X, where X is the number of Slivers on the battlefield.

They Really don't...and it is VERY unlikely for creatures such as Slivers to ever been able to hold a Planeswalker's spark...

On the Card itself the only really cute ability is the one that makes tokens...the other 2 are simply boring

Oh and in the Subtype it is well know from the elimination of Tribal that creature Subtypes in other non creature permanents doesn't work well...the planewalker subtype is always its first name. (Notice at how Karn Liberated's subtype could have been Golem and yet it is "Karn")