What it does
Giga Impact deals heavy Normal-type physical damage, then locks the user into a recharge turn where they can't attack or switch out.
In singles, the recharge turn hands the opponent a free switch or setup move. In doubles, it's worse: your partner is suddenly holding the field alone while the opponent has two Pokémon to work with. The 'Protect the recharge' trick — using Protect on the recharge turn to avoid damage — burns your Protect for no gain. In doubles, Protect is too valuable to spend on damage avoidance.
The math on when this move is worth it: you need to KO the target, and you need the other opposing slot handled by your partner the same turn. If both conditions hold, the recharge turn becomes tolerable. If either fails, you're in trouble.
Who runs it
Diggersby runs Giga Impact (9% usage in Champions). The ability Huge Power doubles its Attack stat, and Normal STAB on top of that means the move's raw damage output reaches one-shot territory against a wide range of targets. The logic is simple: trade one enormous hit for the opponent's biggest threat, then deal with the recharge. It's a last resort button, not a turn-one click.
How to use it
In doubles, you click this when you've read the field correctly: the target dies to this hit, and your partner handles the other slot the same turn. If you can set up that two-slot sweep, the recharge turn faces new switch-ins instead of the original threat — manageable. If you click it and miss the KO, you're sitting dead while both opposing Pokémon act freely.
Timing matters. Late game when the opponent is down to two Pokémon and you need to clean up is the most common correct use.
Tips & strategy
Don't use Protect on the recharge turn unless the situation is truly desperate — you're giving up one of your most flexible tools to avoid one hit. Instead, build the conditions where the KO is reliable before you click the move. Diggersby has other options, so Giga Impact is the emergency nuke, not the default play.