I stick to cards with a mono-black color identity, since cards like Mortify and Tear Asunder get their Disenchant/Naturalize capabilities from their non-black color
Other pumping staples based on the number of auras you control, like All That Glitters and Ethereal Armor, are a low mana value way to get your legendary creature ready to one-shot an opponent with commander damage
Cards like Lord of Extinction are easily able to swell to a point that they kill in a hit
On top of that, Shadow Rider Calyrex VMAX [Chilling Reign] seems like it might work with Gardevoir ex because the synergy of attaching Energy + doing lots of damage usually works out well
Whenever chaos ensues, target player mills ten cards
For example, Restless Reef can mill four cards even if it attacks as a 2/2, and you can pay the to turn it into a 6/6 with deathtouch