Level 16 DiseaseChaos Phage

Stage 0: The target recovers from the disease.
Stage 1: Initial Effect: A slaad embryo is implanted in the target.
Stage 2: The target takes a -2 penalty to Will. While bloodied, the target succumbs to madness and attacks the nearest creature.
Stage 3: Final State: The target dies, and a slaad tadpole burrows out of its skull.
Check: At the end of each extended rest, the target makes an Endurance check if it is at stage 1 or 2.
19 or lower: The stage of the disease increases by one.
20-24: No Change
25 or higher: The stage of the disease decreases by one.

Published in Monster Manual 3, page(s) 179, The Plane Below, page(s) 142, Dungeon Magazine 162, Dungeon Magazine 179.