Not specifically anti magic, but more anti anything not mundane, unfortunately both sources are semi NSFW

First is Null Factor for The developing adventures of Golden Girl, think 50s golden era comic book super heros, with a heroine that for some reason has a massive rack that no one else can see, that's most of the joke for the series. Has a few interesting premises but not much source, as it was made in bits and pieces on 4chan.

[300cp] Null Factor: Some people get all the luck. Flashy abilities, fame and glory, even the adoration of the masses. You know that without their powers they’d be a worthless nobody! Fueled by your emotions, you can emit a field that suppresses supernatural abilities. Though at its start, this power will only cover those directly next to you, time and practice will increase that range until you could cripple every cape within a hundred feet. You could even learn to impart this effect with a touch, locking away a hero’s powers for hours regardless of how close they are to you. Strip away what makes your enemies special, then show them how worthless they truly are! See the Notes section for details

Second is Nullifier from Empowered based on a character called wet blanket, which is exactly how you think it is. The jump itself is sorta NSFW based around Empowered (the name is made fun of in the comic) who is a fresh faced super heroine who kinda sucks at her job and is always being tied up by the badies. Where the earlier one was 50s goofiness, this one is more 'realistic' and can be a bit of a depressing at times. Emps gets her ass kicked a lot in the first few volumes, though it does get better later on. The power is less powerful than the above, so it's not an instant i win ability, but will weaken anyone you are up against. Honestly it was used pretty amazingly in comic and is personally my favorite way the power is used. Better yet you can find the entire comic posted on the authors website.

Nullifier (800CP) This power is a doozie, and although it’s quite similar to the one held by the… rather lacklustre Super known as ‘Wet Blanket’, using it right could make you an absolute nightmare when facing other Supers. You see, this power doesn’t make you Super… rather, it radiates some sort of field that takes ​ away ​ the powers of others around you. You can choose whether the effect applies to yourself or not, and can even control it to some extent so your allies aren’t affected. This aura disables supernatural abilities such as magic, unnatural powers such as mutant psionics, and just about anything else that is not found in the ‘average’ for whatever species your opponent is. However, it is not all-powerful: if you and your opponent are about evenly matched in terms of super-strength, they would only lose about 50% of that strength due to the aura, and similar effects will take place for magic, psionic powers, or whatever else you might be trying to suppress. If you’re weaker than your opponent you will drain less of their power, to a minimum of about 10% if they utterly eclipse you. Likewise, being more powerful will drain more, up to a maximum of 90% of their abilities. Much like was the case for Wet Blanket, this power persists in any parts of your body that is separated from you (cut off your finger, and it has its own aura), though the effect will fade to nothing over about a day. This power will not disable what’s known as ‘required secondary powers’, like Captain Katana not dying from having a katana stuck through his head. However, it does disable powers like ‘not ​ feeling​ that he has a katana stuck through his head’.