Shots
Shots refers to the number of times a ranged unit may fire per battle. Every time the ranged unit shoots during combat it loses a shot. If the unit has a special ability to shoot twice or receives a morale, it loses two shots instead of one. Although the Ballista says it has shots, it cannot run out, and goes into negatives instead of becoming unable to shoot.
Ammo Cart provides unlimited number of shots for ranged units as long as it is in one piece. The shots start to decrease right after the Ammo Cart is destroyed.
4 shots:
8 shots:
12 shots:
16 shots:
24 shots
Arch Mage
Ballista - Shoots twice from Advanced Artillery
Bounty Hunter 
Catapult - Shoots twice from Advanced Ballistics
Cyclops King - Shoots twice at walls
Ice Elemental 
Evil Eye
Grand Elf - Shoots twice
Halfling 
Halfling Grenadier 
Lizard Warrior
Mage
Magog
Marksman - Shoots twice
Orc Chieftain
Power Lich
Storm Elemental 
Titan
Wood Elf
Zealot
32 shots:
Ammo Cart
Level 1
0
5
0
100
0
Move
Size
1
Growth
400
5
Cost
1000
War Machine. Provides unlimited shots to creatures and War Machines.
Ballista
Level 5
10
10
Shots
24
2–3*
250
0
Move
Size
2
Growth
600
650
Cost
1500 2500 
War Machine. Shoots.