The Flame Orb is an Ultra Rarity item in Pokerogue that can be found in Classic Mode, Daily Run and Endless Mode.
Flame Orb Purpose
Flame orbs are for triggering skills that depend on your Pokémon being under a status condition, like Guts (raises attack by 50% Ignores the attack lowering effect of burns), Quick Feet (raises speed.Ignores the speed lowering effect of paralysis), Poison Heal (heals by 1/8th each turn when poisoned), Toxic Boost (raises attack by 50% only when poisoned) and Flare Boost (raises special attack by 50% only when burned). There may be more skills that get benefits from them but those are the ones that came to mind.