What it does
Zero To Hero upgrades Palafin from Zero Form to Hero Form the next time it enters the field after being switched out. That upgrade is permanent for the rest of the battle — no way to reverse it, and it only happens once.
What Hero Form actually means: Attack goes from 70 to 160. That's one of the highest base Attack stats in the game. HP, Defense, Special Defense, and Speed also get notable increases. The typing stays Water, so every Water-type move still gets STAB.
The trigger is strict: Palafin must switch out while still alive. If it gets KO'd in Zero Form, Zero To Hero never fires and you're stuck with the base form for the whole match. That makes protecting the Zero Form long enough to get at least one safe switch-out a high priority.
Who runs it
Palafin exclusively (100% — signature ability). Zero Form exists almost entirely as a delivery vehicle to get Hero Form on the field. The competitive value is in Hero Form: 160 Attack + Jet Punch (priority Water physical move, +1 priority) + STAB creates a late-game threat that's difficult to outspeed or safely wall.
Choice Band on Hero Form with Jet Punch is one of the format's highest-priority damage outputs. Even physical-defensive Pokémon can take a KO-level hit from it.
How to use it
Standard plan: lead or bring in Zero Form Palafin, do something modest (use a support move, switch pressure, stall with Protect), then switch out safely. The next time you need Palafin, Hero Form is what shows up.
Finding a safe switch-out window is the main skill. Against teams that can pressure a switch-out with strong priority or super-effective hits, you need to create that window — use Protect to stall a turn, or let a teammate take a hit to give Palafin room to escape.
In doubles, Fake Out on a partner can freeze one of the opponent's Pokémon for a turn, giving Palafin the window to switch out unopposed.
Tips & strategy
Hero Form + Choice Band + Jet Punch functions as a near-uncounterable cleaner against slower teams. The priority bypass means most revenge-killers can't just out-speed it, and 160 Attack under a Band hits hard enough to chunk even defensive Pokémon.
Hero Form is still physically fragile under sufficient pressure — 100 Defense is decent but not impenetrable. Time the switch-in, don't just throw Hero Form in blindly.
If Zero Form gets KO'd before switching out, Hero Form is gone for the match. Protecting Zero Form long enough to escape is more important than doing damage with it — even one turn on the field and a safe switch is all you need.