Riftbound Empower
None of the 53 cards with Empower print a reminder explaining it, so there is no official wording to quote here. Rather than guess at the rule, the cards themselves are below.
Which domains get it
Which sets print it
Cards that mention Empower
These do not have Empower themselves, their rules text refers to it.
Ambessa - Matriarch of War
When you empower something else, empower me. (I become Empowered if I'm not already.) Disempower me, any rune, exhaust: Ready a unit.
Ambessa - Matriarch of War
When you empower something else, empower me. Disempower me, any rune, exhaust: Ready a unit.
Hextech Formula
This enters exhausted. exhaust: Empower another gear. (It becomes Empowered if it's not already.)
Kennen - Heart of the Tempest
When you play a card from anywhere other than your hand, empower me. [Action][>] Disempower me, exhaust: Give a unit [Assault 2] this turn. (+2 might while it's an attacker.)
Kennen - Heart of the Tempest
When you play a card from anywhere other than your hand, empower me. [Action][>] Disempower me, exhaust: Give a unit [Assault 2] this turn.
Mel - Soul's Reflection
When you empower something else, empower me. (I become Empowered if I'm not already.) Disempower me, exhaust: Give a unit at a battlefield -2 might this turn.
Mel - Soul's Reflection
When you empower something else, empower me. Disempower me, exhaust: Give a unit at a battlefield -2 might this turn.
Mournful Witness
When a combat that I was in ends, empower me. (I become Empowered if I'm not already.) [Empowered][>] I have +2 might.
Profiteer
When you play me, you may disempower something you control to empower a legend, unit, or gear.
Profiteer (Vendetta Nexus Night Promo)
When you play me, you may disempower something you control to empower a legend, unit, or gear.
Renekton - Brute
1 energy: Give me +1 might this turn. When my Might becomes 10 or more, empower me. (I become Empowered if I'm not already.) [Empowered][>] I have [Deflect] and [Ganking]. (Opponents must pay any rune to choose me with a spell or ability. I can move from battlefield to battlefield.)
Renekton - Brute
1 energy: Give me +1 might this turn. When my Might becomes 10 or more, empower me. [Empowered][>] I have [Deflect] and [Ganking].
Every card with Empower
Most expensive first. Prices are Cardmarket EUR.
Akali - Deadly Weapon
Vendetta · 3 energy
no price yet
Akali - Deadly Weapon
Vendetta · 3 energy
no price yet
Akali - Rogue Assassin
Vendetta
no price yet
Akali - Rogue Assassin
Vendetta
no price yet
Ambessa - Respected and Feared
Vendetta · 5 energy
no price yet
Ambessa - Respected and Feared
Vendetta · 5 energy
no price yet
Ambessa - Respected and Feared
Vendetta · 5 energy
no price yet
Ambessa - The Wolf
Vendetta · 4 energy
no price yet
Ambessa - The Wolf
Vendetta · 4 energy
no price yet
Applied Researchers
Vendetta · 4 energy
no price yet
Apprentice Mage
Vendetta · 3 energy
no price yet
Aurok General
Vendetta · 5 energy
no price yet
Baccai Sandspinner
Vendetta · 6 energy
no price yet
Baccai Witherclaw
Vendetta · 4 energy
no price yet
Brutal Hunter
Vendetta · 3 energy
no price yet
Covert Informant
Vendetta · 3 energy
no price yet
Dame the Despoiler
Vendetta · 5 energy
no price yet
Escaped Grayback
Vendetta · 3 energy
no price yet
Frostcoat Mother
Vendetta · 3 energy
no price yet
Gangplank - Naval
Vendetta · 6 energy
no price yet
Gangplank - Naval
Vendetta · 6 energy
no price yet
Glowstone
Vendetta · 2 energy
no price yet
Grumpy Rockbear
Vendetta · 4 energy
no price yet
Grumpy Rockbear (Vendetta Nexus Night Promo)
Vendetta · 4 energy
no price yet
Helm of Suppression
Vendetta · 4 energy
no price yet
Hextech Disc
Vendetta · 4 energy
no price yet
Jayce - Defender of Tomorrow
Vendetta
no price yet
Jayce - Defender of Tomorrow
Vendetta
no price yet
Kayle - Justified
Vendetta · 3 energy
no price yet
Kayle - Justified
Vendetta · 3 energy
no price yet
Kharox
Vendetta · 6 energy
no price yet
Kinkou Lifeblade
Vendetta · 4 energy
no price yet
Legion Marauder
Vendetta · 2 energy
no price yet
Mel - Defiant Soul
Vendetta · 5 energy
no price yet
Mel - Defiant Soul
Vendetta · 5 energy
no price yet
Mel - Defiant Soul
Vendetta · 5 energy
no price yet
Mel - Newly Awakened
Vendetta · 4 energy
no price yet
Mel - Newly Awakened
Vendetta · 4 energy
no price yet
Mel - Newly Awakened (Vendetta Nexus Night Promo)
Vendetta · 4 energy
no price yet
Nasus - Ascended
Vendetta · 8 energy
no price yet
Nasus - Ascended
Vendetta · 8 energy
no price yet
Noxian Emissary
Vendetta · 2 energy
no price yet
Platewyrm Egg
Vendetta · 3 energy
no price yet
Punching Poro
Vendetta · 2 energy
no price yet
Questionable Tome
Vendetta · 3 energy
no price yet
Rage Amplifier
Vendetta · 4 energy
no price yet
Risen Altar
Vendetta
no price yet
Serene Ascetic
Vendetta · 3 energy
no price yet
Shadow Fiend
Vendetta · 2 energy
no price yet
Solari Sunhawk
Vendetta · 3 energy
no price yet
Steel Paws
Vendetta · 1 energy
no price yet
Tail-Cloaked Matriarch
Vendetta · 4 energy
no price yet
Tools of Empire
Vendetta · 4 energy
no price yet