White ignores the witch and just forces the black king to the corner. I'd say 1. Gf4+ is most direct here, but perhaps Ge4+ or even Kg4. I'm certain this is winning for white with ease. 15-20 moves.
Witch in endgame
You may have found a mating technique with the king and guard that requires zugzwang, in which case the witch will make a difference, but mate is easy with simple brute force. The king and guard can easily shepherd the enemy king.
...but if the knight wasn't on c6 (it's on a2 or c2) then the witch is critical,
I think the knight was on a2
Yup, here's a few moves previous in the game:
50.Bh8...Nb1
51.a4...Nc3
52.a5...Na2
53.b5...cxb
54.a6...bxa6
55.Bi7+...Kf5
56.Kg3...b4
57.c6...We8
58.c7...Wc8
Even with the witch, the game went to 78 moves (after Ry issued conditional game endings and Tomato said he accepts the longest one).😅
76.Kj2...i3+
77.Kj3...Kh4
78.Kj4...Qj1#
Good example. I suspect white is still lost even without the witch, I'm guessing the knight was on c6 and black could have played 58... Ne7, but if the knight wasn't on c6 (it's on a2 or c2) then the witch is critical,