Around-ish 2.0 corrupted wolf might have been the last thing you saw 
Truly it was the most scary encounter and also we play with buffed NPC damage set to x2.0 so this guy could 2-hit every player and it’s attacks are quite fast.
As Taemien said there is 2% chance for it to spawn. But first usually you have to kill a wolf and then there is a 2% chance that it’s going to respawn as a corrupted wolf.
When I lived in the woodlands I saw maybe once corrupted wolf spawning after server restart all the other corrupted wolves I saw in past few years were replacing a normal wolf after it was killed.
A PITA challenge truly, and I’m stuck with it for 6 days. They want you to kill three mobs that are not on the map and there is only 2% chance to spawn it.