edhseer Commander synergy, explained
Land
Hideaway 4
This land enters tapped.
Add {U}.
activated {T} — adds 1 mana
You may play the exiled card without paying its mana cost if a library has twenty or fewer cards in it.
Causes: nothing.
Cares about: nothing.
a land enters the battlefield — 1,560 cards in the game can cause this (Shelldock Isle is one).
When Shelldock Isle enters:
199 other cards care about it too. These are the ones with the most connections.