The poison Forest has several unique mobs:
All mobs in the Poison Forest are aggressive to other mobs not native to the Poison Forest, and will attack them on sight. In addition, hostile mobs, utility mobs, wolves, and boss mobs are aggressive to Poison Forest mobs.
The Poison Forest constantly attempts to advance into other biomes through Spore Pods, rolling mushroom block-like mobs which combust, leaving saplings in their wake, and will slowly take over other biomes around them if not burned or destroyed.
In Poison Forests, grass looks blueish and so do non-thorn tree leaves, and water looks purplish. Hostile Mobs will occasionally spawn due to the darkness, or wander in from other biomes. but will be killed by the more aggressive Poison Forest mobs. It should be noted that pigs, cows, chickens, sheep, and rabbits cannot spawn in the Poison Forest.
Rivers may also spawn in the Poison Forest biome, but contain Poison rather than water. It is worth noting that lava cannot generate in the Poison Forest.