Now, overall, this is a pretty darn good add-on. Certainly makes you stress when the message shows up, knowing he's after you. His mechanics are pretty much accurate, so you're basically going against what's advertised.
However, there is one glaring issue that makes going up against this fiend more of a pain that is should - he attacks WAY too often.
While getting grabbed is the main threat, 2011x recovers FAR too quickly for it to be fair. This also makes stunning him pointless, as his recovery time means that, by the time you try getting away through hitting him, he's back on his feet, and probably right next to you - if he hasn't decided to just bomb-rush you instantly, forcing you to take damage.
His recovery and attack speed also makes certain levels far harder than they should - starting as early as Techno Hill Act 1. The purple liquid that lifts you up if you fall into it? 11x only needs a MOMENT to get you in range of a puddle, and suddenly you're being forced into a game of waiting, hoping that shaking out of his grab won't put you below the liquid, as that lets that fiend charge you over and over whilst keeping you bouncing in and out the lake, allowing him to grab you whilst you're RECOVERING.
Here's my overall list of requests to make 11x at least combatable:
1.Stun time changes - escaping his grab should give optimal time to escape, whereas stunning 11x back should keep him laid out for longer (i.e. grab - 5 secs, stun - 7.5 or 8 secs)
2.Teleport timer - since this is mostly based off of OM, 11x should have a limiter on his teleport. Every teleport should restrict him for 20 secs, meaning that, every time he gets stunned, until his time is up, 11x should instead et up and start flying again towards you, allowing the player to make optimal distance between them and 11x, until they get their teleport back and appear behind them. (Speaking of which, 11x spawns inside the player, not behind them. Game wise, this means nothing, but I think it's an easy visual thing to change that'll make sense.)
3.Easier attack - that weird thing he does, where he just charges into you, forcing you to take damage. It's not fun. There should be a way to work against that.
Hopefully, you read through this textbook of a review, and perhaps find a place in you heart to act upon these issues, making this addon even better than it is now.
(P.S. this is just me, but is there a way to make 11x "interactable"? I mean this in the way that, maybe dark sonic (X Sonic) could use his fighting on 11x, or Kou (StephChars) could actually parry 11x coming towards him, since he can only punch him normally. These are personal wants, but it would be really fun if you could do this. Thanks!)