What it does
Reckless multiplies the power of moves with recoil by 1.2×. The recoil itself doesn't change — you still take back 1/4 or 1/3 of the damage you deal, depending on the move. You're buying damage, and you're paying in HP every time you click.
On high base-power moves the math is noticeable. Head Smash goes from 150 to an effective 180. Double-Edge jumps from 120 to 144. One thing to clarify: High Jump Kick is NOT a recoil move — its crash damage triggers on a miss, not on a hit, so Reckless does nothing for it.
Who runs it
Rhyperior at 1% is the only Champions user. That number is doing a lot of work: the standard Rhyperior runs Solid Rock at 77%, because cutting the damage from its quad-weaknesses in half is what keeps it functional. Reckless is a real option but a deliberate deviation from the norm.
How to use it
Head Smash is the main payoff — 150 base power becomes 180, at the cost of 1/2 the damage dealt reflected back. Choice Band pushes the output further if you don't need the flexibility of switching moves, though the HP drain becomes punishing fast.
Protect matters a lot here. You're bleeding HP every turn you attack, so stalling a turn or letting your partner finish something while you recover position is worth it.
Tips & strategy
Reckless Rhyperior and Solid Rock Rhyperior are entirely different Pokémon. Solid Rock is a wall that soaks hits and stays around; Reckless is a spike — high burst, short lifespan. If the opponent survives your first two attacks, you may have damaged yourself into KO range.
Run it knowing the trade-off. A support partner that can heal or redirect is more important here than in most builds.