Mag’har Orc Warlocks

I do not doubt it CAN corrupt but I would not say its as a baseline. But in this example, I would think its more a play on the trope that any magic can damage you, its common in low fantasy settings where over extending yourself magically causes bodily harm. And in the case of life tap, seems to be more a play on blood magic, another ‘forbidden’ field of study warlocks have dabbled in. Warlocks have a few of them such as Siphon life (Which undead pets have as well), and Soul Rot(Nature spell previously granted by the night fae, now a talent).
which is supported by the description in the book Bayond the dark portal

  • Gorefiend tightened his fist and blood suddenly burst from the hapless orc’s nose, eyes, and mouth. Gorefiend had already turned away by this point, having lost interest in tormenting the annoyance. “Dark magic!” one of the Shadowmoon warriors shouted, grabbing up the axe beside him. “Kill the warlocks before they can afflict any more of us!” he bellowed, and his fellows responded by readying themselves as well

And this is one of those things that can be interpreted different ways. The cost doesn’t need to be “FEL CORRUPTION” It could be the cost to ones character. Making it easier to do evil deeds the next time, pushing yourself further and further into more damaging methods because you survived fine previously.

And these are perfectly fine. Said bargain may not be in the warlocks favor. I alluded to it in my post. I think the bargain made by the draenei and gul’dan specifically had a corruptive element added in.
The bargain made elsewhere does not seem to be nearly as damaging.
Plugger Spazzring has had Mistress Nagmara for years now. He and all of Blackrock depths do not seem to be suffering from any fel corruption from whatever deal he made. Nagmara seems to actually enjoy herself as well.

Knowing Warlocks lust for power and how deep the firelands go, I suspect he will find more “corruption” the same way the druids of the flame did and every Dark Iron dwarf with smoldering embers for beards. Its all a sliding scale.

I think this is the key word here. It is not a byproduct. It was the entire end goal of the spell on both timelines. If using it corrupted passively they could have just casted fire spells until the area was green.

I think this can go for nearly everything. It would be hard to quantify this corruption as a physical or mental state. Really he did the same thing Illidan did when he needed more power and got rid of some of the users to fuel his own needs. From their perspective I am sure it was easier to blame the demon. In the context of things was he truly mad? The power was split presumably evenly, by everyone in the city and these pylon were directly responsible for keeping the demon contained. To me it seems he took the hard decision to prioritize containing the demon.

This to can be interpreted differently. The city itself suffers no Fel corruption that we can see. It has been defiled by ogres and left to ruins. Being as this tree is in a Highborn city. I would postulate its one of the Ancient of the Arcane. You see these in the Calderra, Botanica, and Arcosin is just outside in Feralas. We have fel-corrupted treants, but we also have a ton of ‘corrupted’ treants the world over, such as in eversong. Treant corruption seems to be more tied to the health of a location rather than any magical affliction. They are siphoning magic in this city, the wildlife suffers the same as the elves.