Troll

Trolls are fairly normal when it comes to their combat tactics - they mostly just smack you until you stop moving. What distinguishes trolls is their extreme hatred of sunlight, rapid regenerative abilities, and hunger.

Trolls will spawn in caves even in the highest mountains, but only if they are incredibly dark - far darker than even normal monsters can spawn in. Trolls will flee sunlight to the best of their ability, and will be slowed while in sunlight... and also gradually turn to stone. While they are mostly harmless in daylight, they are incredibly dangerous in darkness, where their regeneration will make even the most dangerous of weapons nigh-useless against them. Only one thing is known to overcome their regeneration: fire.

Origin

Trolls are a mix of Dungeons & Dragons (regeneration and weakness to fire) and trolls decribed by J.R.R. Tolkien (turning to stone in the sun).