It's not that difficult to create a card that boosts a specific hero, while being useful but not too advantageous to other heroes it's available to.

I.e.
Stonebreaker Glaive

Type: Item - Warrior Weapon
Cost: 3cc
Attack: 1
Durability: 3
Ability: When your hero kills an ally in combat during your turn, target friendly ally is readied.


Can't be abused by Amber, but may be used. (would have only 3 Attack and 3 durability is not a good investment)

Can combo this with killing spree.

3 cost so: Turn 3 - Play Stonebreaker Glaive Turn 4 - Use Stonebreakers ability + Kill opposing ally + Ready a 4 cost ally you've played this turn.