What it does
Cross Poison is a Poison-type physical contact move with 70 Base Power. Each use raises the user's critical hit stage by one (cumulative), and there's a moderate chance — roughly 10% — to poison the target on hit.
Crit stage starts at 1/24 chance; one stage up brings it to 1/8. The stacking is real across a game, but most Champions matches move fast enough that getting three or more Cross Poison uses off in the same battle is rare. Treat the crit accumulation as a slow bonus, not a strategy you're building toward.
Poison is super effective against Fairy — that's the core reason this move exists on Toxicroak. Against Fairy types, it's the most direct damage option and one of the few STAB hits available. The poison chance itself is just a secondary effect you might get.
Who runs it
Toxicroak is the sole user in Champions at 7% usage. Its Dry Skin ability heals HP each turn in rain, which ties it almost exclusively to rain-team builds. The role of Cross Poison there is to cover Fairy types — Toxicroak's Fighting moves bounce off Fairy, and having a Poison STAB patching that gap is the reason to include it. Both Poison and Fighting are Toxicroak's own types, so Cross Poison gets full STAB.
How to use it
Cross Poison makes contact, so watch for Rocky Helmet and Rough Skin chip coming back at you. In rain, Toxicroak's HP is regenerating every turn via Dry Skin, so minor recoil is usually fine — but it's worth tracking over a longer game.
Point it at Fairy types. When you see Togekiss or Sylveon across from you, Cross Poison is the direct answer. Don't overthink it.
Tips & strategy
The 7% usage rate reflects what this move actually is: highly specific coverage that exists for one purpose. If the opponent's team has no Fairy types, Cross Poison loses most of its value. When building with Toxicroak, you're accepting that this slot is almost dedicated to Fairy matchups.
Don't design turns around hoping for a poison proc — the chance is low enough that betting on it is rarely correct. The crit stacking is a similar story over short games. Use Cross Poison for the reliable Fairy damage it delivers, and treat the status and crit bonuses as upside.