Eiganjo Castle

damage is prevented — 568 cards in the game can cause this (Eiganjo Castle is one).

When a creature has damage prevented thanks to Eiganjo Castle:

1. Phyrexian Vindicator — deals that much damage
2. Selfless Squire — puts that many +1/+1 counters on itself
3. New Way Forward — deals that much damage
4. Samite Ministration — gains you that much life
5. Judgment of Alexander — deals its power damage

a land enters the battlefield — 1,560 cards in the game can cause this (Eiganjo Castle is one).

When Eiganjo Castle enters:

1. Primeval Bounty — gains you 3 life
2. Toph, Earthbending Master — puts a counter on a permanent
3. Dancing from Dark to Dawn — makes a token
4. Emeria Shepherd — brings a card back
5. Quest for the Necropolis — puts a quest counter on itself
6. Soul Stair Expedition — puts a quest counter on itself
7. Nissa of Shadowed Boughs — puts counters on a permanent
8. Thranduil, Sindarin Liege // Silvan Rally — makes a token
9. Silvan Reveler — returns itself from the graveyard
10. Floral Evoker — puts a +1/+1 counter on itself

199 other cards care about it too. These are the ones with the most connections.