Bunch of people hyping it, what can you use to counter it?
Don't believe the hype; look for people actually explaining what makes it so good... which will also help you find counters.
Right now, you've got a
lot of options. The first is... nothing.
Raichu-GX is a Lightning-Type Stage 1 with 210 HP, Fighting Weakness, Metal Resistance, Retreat Cost [C] and three attacks: "Powerful Spark" requires [CC] and does 20 damage plus 20 per [L] Energy attached to
all of your opponent's Pokémon in play, "Thunder" for [LLC] which does 160 to the opponent's Active and 30 to itself, and the GX-attack is "Voltail-GX" - also for [LLC] - and does 120 damage plus guaranteed Paralysis. Your opponent requires a
Wally to get it to the field on his or her first turn, which probably isn't worth it as the card needs
support to do anything impressive. That gives you time to
wreck that setup, or at least shoot for an early lead to blunt the drawbacks of a strong performance.
Except I don't expect that strong of a performance.
Powerful Spark resembles some successful attacks
but the specifics of those cards (like being a Basic with good HP) or of the support behind those decks makes a
big difference. I think it will result in at least one competitive deck
but if your deck isn't Lightning Weak or
incapable of scoring a OHKO against
Raichu-GX, the deck is probably fine as is. AFter that, consider any Fighting-Type that could work its way into your deck - like
Marshadow-GX -
or stopping Abilities, as those are probably the only way to make
any of the attacks worthwhile.