edhseer Commander synergy, explained
Land
If you control two or more other lands, this land enters tapped.
static —
Add {G}.
activated {T} — adds 1 mana
Until end of turn, this land becomes an X/X green Hydra creature. It's still a land. X can't be 0.
activated {X}{G} — turns something into a creature
Causes: nothing.
Cares about: nothing.
a land enters the battlefield — 1,560 cards in the game can cause this (Lair of the Hydra is one).
When Lair of the Hydra enters:
199 other cards care about it too. These are the ones with the most connections.