edhseer Commander synergy, explained
Land
Add {C}.
activated {T} — adds 1 mana
Add one mana of any color. Spend this mana only to cast an Assassin spell or a spell that has freerunning, or to activate an ability of an Assassin source.
activated {T} — adds 1 mana
Causes: nothing.
Cares about: nothing.
a land enters the battlefield — 1,560 cards in the game can cause this (Brotherhood Headquarters is one).
When Brotherhood Headquarters enters:
199 other cards care about it too. These are the ones with the most connections.