Black is the color in MTG that specializes in discard spells, creature-killing spells, reanimation spells and cards that are generally oppressive to play against (and some cards that are actually Oppression in cardboard form)
I took it apart for parts a couple of weeks back, and when looking for new Temur commanders printed this year, was dismayed to find that Miirym was ituntil the Tyranid Swarm is available
Kess, Dissident Mage Cards that let you play spells from your graveyard have always been well-liked in Magic
Since all the combos require my commander to instantly win, a quick n' easy way to do this would be just to swap Niv-Mizzet, Parun out with a noncombo commander and call it a day: Niv-Mizzet, Dracogenius is a straightforward swap if you still want to keep The Firemind in your command zone, or you can switch to another Spellslinger commander like Kaza, Roil Chaser
The magnification of the cards is also off
The severity and area affected can vary, significantly impacting the cards condition in grading