What it does
Heatproof has two effects. Fire-type moves deal half damage (×0.5). And if the carrier has the Burn condition, the end-of-turn HP loss is halved — from 1/16 max HP down to 1/32 per turn.
The burn half-damage note: burn's physical damage penalty (halving the attack stat's effective damage output) still applies normally. Heatproof only reduces the chip, not the stat penalty from being burned.
Against sun teams, the math shifts noticeably. Sun already boosts Fire-type moves by ×1.5. Heatproof cuts that in half, so you're effectively taking around normal levels of damage from sun-boosted Fire attacks instead of the ×1.5 multiplied version.
Who runs it
Sinistcha is the only Champions carrier, at roughly 1% usage. Hospitality delivers value in every game regardless of the opponent's team. Heatproof only earns its keep when the opponent is running Fire-based offense — and most of the time they aren't.
The exception: if you're specifically preparing for a sun-heavy meta or an event where Fire attackers are common, Heatproof Sinistcha is a legitimate anti-sun piece that can set up Trick Room without getting cleared by Heat Wave.
How to use it
The core gameplan is the same as Hospitality Sinistcha — Trick Room support, Follow Me, draining moves. The difference is purely defensive: against Fire-focused leads, this version is harder to KO in setup turns and can set Trick Room more reliably.
In a matchup where you know the opponent leads Fire attackers, Heatproof turns a potentially difficult setup turn into a comfortable one. The opponent's Sun Heat Wave doesn't threaten a KO, and Sinistcha completes its job.
Tips & strategy
Sinistcha is Grass/Ghost type and already has a ×0.5 type resistance to Fire. Stack Heatproof on top and Fire moves deal ×0.25 total — that's four times normal resistance. Even sun-boosted Fire moves can't easily break through.
If the opponent uses a burn (Will-O-Wisp) on Sinistcha, the physical attack penalty applies normally. Heatproof cuts only the per-turn HP drain. Don't mistake it for burn immunity.
In games without Fire threats, this ability is completely silent. That silence is why Hospitality is the right default for most team builds.