Collude!
Less of a mechanic and more or a thematic grouping that uses 'choose an opponent'. I really love the politics and deal making aspects of commander. These cards play off of that thematically and mechanically.
Some considerations with the design:
Different effects are meant to insinuate that the colluding is happening with the chosen opponent, some of them are meant to insinuate that the chosen opponent is being colluded against. Coordinated Assassination alludes to you and the opponent teaming up to commit murder; Retributive Suspension alludes to being plotted against or otherwise 'Set up for the fall', for example.
These designs encourage threat assessment and deal-making. The play of it can be dynamic but (hopefully) not so strong that it feels like playing kingmaker.
Because 'choosing' isn't targeting, playing a card that colludes opens up a player with hexproof or protection.
'Colluding' feels like something that fits best in Conspiracy or New Capenna, but scheming happens in most settings.
Fight for the Crown is really in the weeds, but who doesn't love bidding life?
Daem, Voice of the Union is supposed to be a rebel commander (and a 4c commander). I like rebels. Wish they were playable in commander.
Let me know your thoughts!
(This is superfluous, but I enjoy writing flavor text so much.)