What it does
Accelerock is a +1 priority Rock-type physical move. +1 priority means it goes before any non-priority move, no matter how fast the foe is — as long as neither side throws higher-priority.
That's the whole pitch: not enough Speed, so let priority make up the gap. A Pokémon that would normally get out-sped by an opposing sweeper instead clicks Accelerock and removes that low foe first. Rock hits Flying, Fire, Bug, and Ice for double, and a lot of fast sweepers fall into those types, so Accelerock often takes them out before they move.
Know the priority ladder: Accelerock is +1, so anything +2 or higher beats it. An opposing Fake Out at +3 resolves before your Accelerock. Two moves at the same priority (both +1) then sort by normal Speed.
Who runs it
Lycanroc is the carrier, at 47% usage. It's a fast Rock-type already, so adding a priority Rock move stacks an 'ignore Speed entirely' finisher on top of its natural Speed. Even against something faster, or after getting slowed, or under Trick Room, Accelerock still lets it land Rock damage first.
How to use it
The classic use is cleanup. A foe is in the red and might switch out or revenge-kill you next turn — Accelerock jumps in before it acts and finishes it.
Its value climbs in doubles, where the Speed picture is messy — Tailwind and Trick Room both scramble the move order. Accelerock ignores all of that; at +1 it still moves first. If the foe sets Tailwind to steal Speed, Lycanroc's priority Rock hit still pressures their Flying or Fire sweepers.
Note that Accelerock is single-target, not a spread move, so it skips the doubles ×0.75 cut and hits one foe for full damage.
Tips & strategy
Low power is the real catch — priority moves hit soft across the board, and Accelerock is no exception. It's a finisher and a tempo tool, not your main damage source. Don't expect it to punch through a healthy target.
Queenly Majesty and Dazzling shut off every priority move. If a Tsareena with Queenly Majesty is on the field, Accelerock aimed at it or its partner gets blocked, and that turn is wasted.
Against Focus Sash or the Sturdy ability, Accelerock won't finish a full-HP target — the sash or Sturdy leaves it on 1 HP. Knock it out of full first with another move, then clean up with Accelerock.