I figure it's more realistic to create new cards base on the current available functions / keywords etc. So I'll throw in some here, feel free to discuses them.
Blood Mage
Rare
Cost: 20 Gems
Keyword: Alliance, Mage, Banish
Attack: 20
Steals the difference between your Gems and enemy's Gems (Max 20)
(Concept: Assuming Mountain King is from Warcraft 3, I picked the hero Blood Mage and utilize his in game skill of Banish / Siphon Mana into MAcromage functions)
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Mortar Team
Uncommon
Cost: 10 Bricks, 10 Recruits
Keyword: Alliance
Mode 1: Enemy wall -10N
Mode 2: Attack 4N
where N = #Alliance cards in your hand (max 5)
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Dwarven Rifleman
Common
Cost: 2 Brick, 2 Recruit
Keyword: Alliance
Enemy tower: -5
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Priest
Common
Cost: 7 Gems
Keyword: Alliance, Holy
Stock +N/2
N = #Holy and Alliance cards in hand (rounded)
If last card played was a Holy / Alliance
Wall +5