I somewhat dislike the card for being so good verses some colours while fairly average against others but that is exactly what decks like reanimator want, a few silver bullets that are really likely to take the game solo which this achieves perfectly
Olivia, Crimson Bride Olivia, Crimson Bride is a vampire commander with flying and haste that lets you put a creature into play from your graveyard tapped and attacking whenever Olivia attacks
Yes, thanks mostly to contributions from Jumpstart and Jumpstart: Historic Horizons, there are a couple dozen slivers on MTGA
Kethek, Crucible Goliath Kethek, Crucible Goliath offers a fun type of sacrifice commander that can also help you take out your opponents creatures
RB decks need Bedevil and Embereth Shieldbreaker, WB decks need Heliods Intervention, and Jund decks need Gemrazer or Thrashing Brontodon