Black is the lightest of splashes mostly so I could run Spectral Procession without much risk
Congregate | Rarely going to be too valuable / too situational Boros Guildmage | Use a Dragon Tempest or something, creatures too easy to remove, and mana sponges One or a couple of these should get you Kiki-Jiki, Mirror Breaker in there
Over on the forced combat side of things, Combat Calligrapher, Tomik, Wielder of Law, and Nils, Discipline Enforcer all feel pretty underwhelming
the first of these is Aetherworks Marvel, a Legendary Artifact that can be cast for four generic mana
Players can use it to store their Azurite Seas hauls, or a larger collection of Lorcana sets, using its sleeves to display and organize cards