I believe Master of Souls is a great Variation. Soul Ball capture leads to a solid 50/50. Almost every touch can convert into a 35-40% combo (often meterless) with meter he can do upwards of 46% (Not worth it imo) He has quick strings with an 11 frame and 12 frame punish. A 6 frame d1 and a d3 that is very solid.
*Note F2 D1 2 isn't completely safe as some characters can armor through it
Where Ermac falters is, how unsafe he is. Every special in his arsenal minus ex air blast is combo punishable on block from up to sweep distance. His teleport is so slow it's almost comical (25 frame startup) However it can lead to massive damage on hit, so that's a fair trade I suppose.
He is a bait & mind game character. If you guess wrong, he will make you pay for it, although that's a mute point since that is a trait shared by damn well everyone.
He has no good reversals. Ex Teleport only has Armor off of wake up...I don't know why someone thought that was a good idea when countless character's moves have armor in general. Keep the move as unsafe as it is (-17) but give it armor for ex in general. Ex Soul Blast, some have already mentioned has a faulty hitbox. Here is a demo taken from one of my early matches:
No slide, no low profile. Simply moved forward, ex soul ball whiffed completely.
In summary, I think MOS needs very minor, minor tweaks. Hit box issues.
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Mystic needs help. This is on paper, supposed to be Ermac's Zoning variation. Yet, for the variation that is supposed to focus on how good his TK moves are, all of them are horrendously unsafe on block. TK Push means nothing when someone can run cancel to block and be right back in your face. (Personal gripe) Also, the variation has no real damage, at least not compared to Master of Souls. Given that this is "zoning" I'd be accepting of that if the zoning moves were actually...good. Make his TK moves less punishable on block and this would be fine. Or throw the armor on ex Tele Lift....something. A damage boost? Anything really.
Spectral: Trying to break down Spectral would take a book. This variation is useless. Recovery on flight, not being able to block in the air. He flies slow. Is prone to uppercuts the moment he goes in for pressure, the normals aren't very good and have awkward hit boxes. He needs meter to do anything even remotely damaging. He can't air dash....I don't know why.
Honestly, I shouldn't have been surprised. As I recall when they showed off Spectral on the stream it got no real attention. It was like, "here he can fly, not hover. Look at him float and use interactables in the air.....and we're done." I expected Spectral to have some Marvel esque combos. Which you can get in the corner. NJP, flight, 1, 1, 1, 1, 1, air blast....woo fun.
This variation needs help, I think the general Ermac community just pretends it isn't there. Only person I've seen use it is K Frog. Best thing I can say about Spectral is the Soul Crusher has 10 frame startup. Never mind the fact it's -23 on block and has no armored variant. It can be used as a decent punisher.