When in the AU Draenor, we see that in the background there was another looming threat besides just the Iron Horde and the Legion: the Zangar Encroachment.
This mushroom invasion was everywhere from Nagrand to Tanaan and as far as we know, it may still be invading and causing problems for Yrel and her light army.
Aside from its invasion, we can see it has different effects on different species, evolving the podlings into intelligent sporelings but infesting the orcs and goblins, turning them into mindless zombies.
In terms of weaknesses, we saw very little, with it seemingly being only weak to fire. The Zangar shrooms even managed to thrive in the face of Draenor’s destruction, turning the bed of the Zangar Sea into a thriving ecosystem with a variety of spore-based life that wasnt previously present on the planet. That said, this did seemingly stop the outward spread of the mushrooms.
If the planet hadnt been destroyed, could the orcs have accidentally brought the invasive fungus to Azeroth while their own world was being consumed, leading to Azeroth being taken over by the Encroachment?