Something has always fascinated me about the concept and symbolism of fire while corruption and savagery in games (unless I am the one spreading it) has always triggered some primal disgust. The xenofloral fungus in Terra Invicta. Corruption in Total Warhammer. Savagery/spreading evil in Terraria/Dwarf Fortress.
And thus pole plants, monster kelp, worm grass, and the rot all bring out the exact same feelings.
The purifier is a candle slugcat that uses the fire on their head as a pilot flame to start raging wildfires to turn the nightmares of Rainworld to ash. From the fire, like the phoenix, the mundane and benign can grow. Wielding purifying flames the vile corruption of rot can be burned away and the inert ashes fertilize new life.
Rebirth. Renewal. And a safer world.