Troll is a creature type.
They are a mainly red and green creature type represented in the Magic lore as large, bestial, ill-tempered humanoids that usually dwell in forests and have regenerative powers.
The Trolls who were brought to Mirrodin lived at Tel-Jilad, the largest tree in the Tangle. Inscribed onto its metal surface is the history of Mirrodin. Near the bottom, all the writings have been etched out. The trolls considered this their sacred home, and they lived within its hollow core. After the Vanishing there was only one left: Thrun, the Last Troll.
On Ravnica Trolls are hunted and experimented on.
Trow are the vile Trolls that lurk in the bogs of Shadowmoor. They reappear each night to frighten the living and gnaw the dead.