1. They explode (cos their bodies can't convert to vitamin D when exposed in sunlight),
2. Oftentimes, they turn to stone when they're older and their bones expand inside their bodies that their veins become to narrow.
3. They EAT people who have Christian blood... Ha, Anti-Christian Trolls eh?
4. Some can grow 2 more heads like the type in Greek myths of Hydra and Cerberus.
5. Any weapons like HUUUUGE spotlights and bazookas can easily kill them.