Though these trees slumber fitfully through the cycles of the world, nearby use of magic infuses them with bloodlust...
Source: Warhammer Fantasy: 8th Edition
Blood ForestURL Copied!
Whenever a spell is successfully cast by (or at) a model in a blood forest, all units wholly or partially within it suffer D6 Strength 4 hits as the trees go into a feeding frenzy.
When any hits have been resolved, the Blood Forest moves 2D6" in a random direction, moving around any intervening terrain features by the shortest route. This does not move the models that were in the Blood Forest, it simply 'walks' off, and leaves them behind.