edhseer Commander synergy, explained
Land
This land enters tapped.
Add {U} or {B}.
activated {T} — adds 1 mana
Until end of turn, this land becomes a 3/2 blue and black Elemental creature. It's still a land. It can't be blocked this turn.
activated {1}{U}{B} — turns something into a creature
activated {1}{U}{B} — restricts what can block it
Causes: nothing.
Cares about: nothing.
a land enters the battlefield — 1,560 cards in the game can cause this (Creeping Tar Pit is one).
When Creeping Tar Pit enters:
199 other cards care about it too. These are the ones with the most connections.