Blood Sado
Type: Shadow Ally - Ravager - Unique
Cost: 4
Attack: 2 (Sword)
Health: 4
Ability: When a friendly hero or ally is dealt damage by a friendly hero or ally, draw a card (max 2 per turn). Friendly ravager allies have +1 health.

Comparable 4 cost allies that generate cards. The above card is a lot more difficult to establish card draw hence the allowance to possibly draw up too 2 cards.

Stardust Extractor Elemental Ally 4 2 6 Steadfast. 0SE: Stardust Extractor's health is reduced by 1 and you draw a card.

Elizabeth Winterborn Priest Ally Unique 4 0 5 Elizabeth has +2 attack while damaged. When you end your turn while Elizabeth is undamaged, draw a card.