I don't think any1 on RU-vid has footage of this special intro, not even mhsanchez Thanos by CPoC & Splode Onslaught MVC2 by XSlaught 2022 11 02 03 49 56
It's the last version of XSlaught's MVC2 Onslaught, configured to use both forms in each round. It's better than any other mugen match you'll see featuring Onslaught. (Except for an accurate MVC1 Onslaught)
