Asriel vs the MCU universe, mostly because Scarlet witch cannot beat Asriel by herself. No matter how much times she manipulates reality, Asriel can do more. No matter how many attacks she throws at him, Asriel invincible. Asriel is practically a stronger version of scarlet witch. The only difference is that he is not feminine and has a weaker soul. Other than that, Asriel is pretty much a absolute Murder.
I would be surprised if Madara v Aizen didn't happen. They have talked about it as being a good matchup in the Death Battle Cast multiple times in multiple episodes.
Martian Manhunter vs Korosensei
Aang vs Naruto
Luffy vs Plastic Man
Sub Zero vs Queen Esdeath
Frieza vs Meruem
Gon vs Deku
Raven vs Scarlet Witch
Meliodas vs Thor
Goku vs Saitama
Hulk vs Saitama
Goku vs Doomsday
Batman vs Johnny Cage
Aang vs Naruto
Luffy vs Plastic Man
Sub Zero vs Queen Esdeath
Frieza vs Meruem
Gon vs Deku
Raven vs Scarlet Witch
Meliodas vs Thor
Goku vs Saitama
Hulk vs Saitama
Goku vs Doomsday
Batman vs Johnny Cage
2.Naruto
3. Luffy
4. Sub Zero
5. Frieza
6. Gon
7. Scarlet Witch
8. Thor
9. Goku
10. Hulk
11. Doomsday
12. Batman