Cool Game, but the fact that i saw the enemy have way more than five barracks and constantly spewing out shit units tipped me off to the imbalance between the NPC enemy and yourself. sure, you can make way better units than them with a good enough economy and good cards.. but it doesnt matter when in the same turn you get 3 Infantry the enemy makes 7 Riflemen.
Overall, good game. bad balance.

player tower don't shoot arrow.
don't play mission when you just start the game, Viking AI is definitely cheating asf.
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finally beat viking, AI can unleash commander AND set up buildings
my deck: 2 lumber mill, 1 barrack, 2 hellhound, 1 giant turtle, 1 cannon, 2 imperial inf, 2 imperial sniper, 1 war bonds.
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Limit high cost cards to 3 so you don't stuck with high cost cards too early, for this deck, the 10+ cost card are barrack, cannon and giant turtle. which means you will never stuck.
Barrack work with lv1 units, so you are able to hold the line with number. You don't have to use the same as mine, but some melees ones are too weak to hold the line, and they don't always gets to return damage due to short range, especially when advancing blindly.
I am thinking about replacing cannon with another lv1 unit, its firepower are good but health is low for its price and being lv2.
Hellhound is lv1, quick, melee with a huge aoe if crowded.
Imperial sniper can easily get in range.
Turtle is the bulk and riot control tank, it will assist your from midlane to enemy base, no other super heavy and high cost are a match for what it can do.
For late game, only lumber mill, war bond and barrack (4) will cause another stuck, lumber mill when placed to the front can absorbs enemy damage, so only barrack have no use.

upgrade card is a terrible idea, it needs a prerequisite otherwise useless and stuck on your hand, many of them high cost.
--beat the other two commander
Apprentice is good. One of my favorite support.
new deck: 2 lumber 2 warbonds, barrack, turtle, 2 Apprentice, 2 imp sniper, 2 imp inf.
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fire spawn attack do nothing