What it does
Hyper Beam hits for massive special damage, then forces a recharge turn where you can't attack or switch out. It's the special equivalent of Giga Impact — same mechanic, same tradeoff, different stat side.
The recharge turn is the entire cost. In doubles, you're effectively removing one of your Pokémon from the field for a turn — it's still there, but it can do nothing, and it can't leave. Both opposing Pokémon can freely pile on, set up, or position. That's not 'a little slow' — that's a full turn of uncontested action handed to your opponent.
Who runs it
Sylveon (30% usage) is the recorded carrier. It's a Fairy-type with very high Special Attack, and while it doesn't get STAB on Hyper Beam (Normal doesn't match Fairy), the raw 150-base-power output is still substantial off its high Special Attack. In doubles, a partner running Fake Out can lock one target while Sylveon fires at the other, making the recharge turn survivable if the Fake Out target is already in a bad spot. It's not risk-free, but it's manageable with the right support.
The 30% usage means roughly a third of Sylveon sets carry it as a finisher option, not a staple.
How to use it
Only click Hyper Beam when you're confident the hit secures a KO and you either win the game on the spot or have a plan for the recharge turn. The clearest use case is end-game: the opponent is low enough that Sylveon can finish them, and after the KO either the game is over or only one Pokémon remains with nothing to punish the recharge. Clicking it mid-game with two healthy opponents on the field is handing them a free turn.
Tips & strategy
The opponent can use Protect on the recharge turn to waste the hit entirely and then punish you — that's a real counter to this move. In doubles, if you miss or the target survives, you lose the recharge turn without the payoff.
Think of Hyper Beam as the nuclear button on Sylveon's set. Moonblast is the safe repeatable attack; Hyper Beam is what you pull out when you need something gone right now and can accept the cost.