Since Raichu can deliver a very solid 140 damage via Thunderbolt, he's used in the Pikachu ex/Zebstrika deck as insurance in case you end up requiring a bigger offensive blow at any given point.

Pikachu ex makes a great contender for this role, due to having a solid 120 HP, but more importantly, the ability to deal 150 damage in a single turn through the Thunderbolt attack.