Staying true to alternating between champion and keyword revealed, Riot showed Monday the third new keyword that will be coming to Legends of Runeterra with the Call of the Mountain expansion. 

The "Nightfall" keyword triggers when this is not the first card you play this round (not counting your opponent's cards). We've only seen three cards with Nightfall so far — Stygian Onlooker, Doombeast, and Duskrider (see below) — and the effects are nice, but not game-breaking. Stygian Onlooker, for example, is a nice 2/1 for 1-mana that is a vanilla creature when played on Round 1 but is a 4/1 Fearsome unit for one round when played second, and that's quite the damage.

If Nightfall cards end up powerful, they will likely birth decks that are less about playing on curve and more about playing for synergy. It could mean a new era for Shadow Isles aggro too, which are decks relying primarily on cheap spells and units, which would allow the necessary mana reserve to play several cards in a round and trigger Nightfall consistently.

A total of five new cards were shown today.

Stygian Onlooker

• Shadow Isles follower
• 1 mana
• 2/1
• Nightfall: Give me +2/+0 and Fearsome this round

Dooombeast

• Shadow Isles follower
• 3 mana
• 3/2
• Nightfall: Drain 2 from the enemy Nexus.

Duskrider

• Shadow Isles follower
• 5 mana
• 2/5
• Fearsome
• Nightfall: Grant me +1/+0 for each time we've activated Nightfall this game

Passage Unearned

• Shadow Isles Fast spell
• 3 mana
• Obliterate all units that were summoned, but not played, this round

Encroaching Shadows

• Shadow Isles Burst spell
• 4 mana
• Grant ALL allies in deck and hand +2/+2 and Ephemeral

Call of the Mountain drops August 26.