You learn anchor magneto by learning magneto himself, in any position, imo.
he’s just a fundamental heavy character, marvel-wise, and you’ll be relying solely on his versatility to win, no bullshit to abuse, just outright being better.
Your main tools by yourself are throw, boxdash L.Blast, cr.L, cr.M, st.L, tri.j.L and fullscreen disruptor snipes. anything else is either unsafe or too slow to risk if you’re in a do or die situation. You pretty much use these 7 tools in conjunction with his great movement to slowly but surely mount your comeback. any hit is at least 600k solo. off of throws, if you dont have xfactor or lvl3, you should do a hefty combo and then snap to get an incoming mixup (because solo resets are not that good in this game, what with all the different teching options, you risk losing momentum, positioning and/or getting randomly footdive’d, helm breaker’d or thrown).
Sorry if this is not very helpful, but he’s not very flowcharty as an anchor, compared to Vergil, Strider, Phoenix, so I can only tell you general stuff.
And yes, grab does become more important when most of your other options are unsafe without assists, if the opponent is looking for them/mashing like a maniac and gets lucky.
PS.: This was mostly posted thinking of a solo, no xfactor magneto. If you have xfactor, you get to go A LOT more HAM with your shit. J.H and S become godlike, tri.j.L becomes insanely hard to block, you can kill quickly from ANY touch (seriously, any touch, anywhere), etc etc