If your commander is a card that has no colors in its color identity, Arcane Signet's ability produces no mana
What you pay into it, it goes away though
The simple ability to cast a bunch of free spells is something thats worth building around, and its worth putting Abaddon into other decks too
-1 Morbid Opportunist: Good card but similar to Elas, I want to focus on ETB and Attacking rather than killing -1 Paladin Elizabeth Taggerdy: I don't want many of my creature cards attacking and honestly the CMC of many of my creatures doesn't make this card worth it -1 Pitiless Plunderer: Same as Morbid -1 White Glove Gourmand: Ended up being a card that read: 4 mana create 2 humans, which is not ideal Artifacts -1 Ashnod's Altar: Never really panned out how I wanted it to, make room for better cards Enchantments -1 Battle of Hoover Dam: Choosing NCR runs into the same issue as Alesha and Desmonda, choosing Legion is fine but also not amazing
The first one is well addressed by bracketed play through the restrictions on combos and a lower overall density of extra-turn effects
Removing creatures (or other permanents) one at a time becomes quite the hassle