>>5981
>If this ring blocks magic how is able to cast spells

Similar to how shade-5 "blocks light" but only really the red part of the spectrum, the "anti-magic" rings of this universe just block "friendship-enforcing" and the further you get from that "wavelength" the more energy that will pass through.
Other parts of the multiverse don't have that distinction, so it just blocks all magic, although if he really goes for universal hope (err, that's hopping. Trot on...) maybe different particulars will be seen in different places -- some places it acts like ear plugs, blocking the first 39Db of energy but a strong enough attempt can "shout" through it ... other places have that metal, but it doesn't involve itself with magic, so he looks funny for wearing a screw-on valve but that's the extent of it.

I do like your idea of involving the alicorn amulet. Because its curses are a little nonspecific aside from some form of insanity, perhaps it's an evil alternate-world Cadance who, having ruined her own world, is trying to break into the nearest neighbor.
Or too, perhaps this world doesn't have changelings, and they're not ... from the blasted wastelands, but again a neighboring universe.
The HLF can bring their small army of unicorns with human personalities into the battle to hold back the horde, and Fred can venture into their lands