edhseer Commander synergy, explained
Instant
Mana cost: {U}
Counter target noncreature spell unless its controller pays {1} plus an additional {1} for each creature in your party.
on-cast —
Causes: counter an artifact, counter a battle, counter an enchantment, counter an instant, counter a planeswalker, counter a sorcery.
Cares about: nothing.
an instant is cast — 3,931 cards in the game can cause this (Concerted Defense is one).
When Concerted Defense is cast:
427 other cards care about it too. These are the ones with the most connections.
anything is cast — 31,128 cards in the game can cause this (Concerted Defense is one).
When Concerted Defense is cast:
5 other cards care about it too. These are the ones with the most connections.