Riftstone Portal

a land it grants abilities to — 1,237 cards in the game can cause this (Riftstone Portal is one).

Riftstone Portal gives:

1. Umara Wizard // Umara Skyfalls — an extra ability
2. Storm the Vault // Vault of Catlacan — an extra ability
3. Sunken Palace — an extra ability
4. Path of Mettle // Metzali, Tower of Triumph — an extra ability
5. Dalkovan Encampment — an extra ability
6. Dowsing Dagger // Lost Vale — an extra ability
7. Dragon-Cursed Halls — an extra ability
8. Pinnacle Monk // Mystic Peak — an extra ability
9. Blackbloom Rogue // Blackbloom Bog — an extra ability
10. Malakir Rebirth // Malakir Mire — an extra ability

1,226 other cards care about it too. These are the ones with the most connections.

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

When Riftstone Portal 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

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