Mephisto by Demolij

Mephisto is a unique support designed to shut down enemy damage dealers while assisting his own. Head on, Mephisto is rather weak, but his ability to indirectly support his allies can be very strong in certain circumstances. Animosity is excessively powerful, reducing the effectiveness of enemies when you fight them, but you actually need to deal damage for it to have any effect and your attacks have very short range. Luckily you can be decent at defending yourself if need be, and have potent cc for handling divers. He works best as a support alongside a single strong damage dealer and likely another support, or against the same. Also, since Mephisto has a very strong base kit all of your talent selections have a trade-off of some kind, but also have a strong benefit involved to make up for it.

Ghastly Skull can be a little hard to land since it isn't very fast moving but the retargeting feature is really effective for sneaking it past the frontline to land a punishing blow on their backline, all the while applying Animosity at range. It's also a potent peeling tool and can surprise juking Illidans with a turnaround shot. Evil Force is a very very spammable skill that deals damage and heals, but needs to be used smartly especially due to the fact that the spirits move very very slowly. The healing and shields are rather small but are one of your only healing tools, but if it hits enemies it also slows their attack speed substantially. Soul Pact is really strong, providing a large damage boost and lifesteal for all kinds of damage the target can put out, but it also reduces their durability slightly so don't be frivolous with it. Place it on someone that's unlikely to get bursted down, such as on a mobile carry that could use the lifesteal, or on a safe mage that you can quickly remove it from if they get dived. It's also really good for capturing mercenary camps and can be self cast for some soloing benefit.

Dark Covenant is a versatile ability that denies the enemy in every way. The shield lasts a long time and isn't a massive thing, so if the enemy wants to they can focus someone else in the meantime, but if they decide to burn through the shield they will be surprised by a chunk of damage and disable. It's excellent against burst comps. Demonic Possession is a weirder ability that might seem less competitive, but given how weak you are to dive being able to become intangible is pretty good. You can cast abilities and basic attack with impunity, and you will deal free damage to the Host passively and with Evil Force (you can't basic attack the host though). This comes with the downside that you are at the mercy of the host meaning they can put you out of position, but you can instantly escape a pretty sizeable distance away from them if necessary. Both heroics have quite short cooldowns so use them often!