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Light type
Offensively it is good against Dark, Fairy, and Ghost.
Light dispels darkness, exposes fey trickery, and wards off ghosts.
Offensively, it is bad against Fire, Grass, Ice, and Water
Fire is already bright so shining light on it won't do much, Light just lets plants Photosynthesize easier, and water refracts light to weaken it. Ice is just frozen water so it gets the defensive bonus too.
Defensively Light is good against Dark, Ghost, and Bug
Darkness is dispelled by light, ghosts attacks are stuff like Shadow Ball/Claw/Sneak/Punch etc. and light weakens shadows, Bugs are attracted to light so they don't hit it as much.
Defensively, Light is weak to Fire, Grass, and itself.
Light and Fire are super effective because they shine brighter and envelope the light. Grass is super effective because approaching a light will make it healthier and stronger for the attack.
Lanturn is the only pokemon retconned to being Water/Light. No old moves become Light type, not even Solarbeam/Blade or Tail Glow. We have to make new pokemon and new moves to support this.
