I have found an inaccuracy in the listing of some of the items that spawn new units. The number of creatures you get is random. This is what I have found out so far:
Carved Coffin  Each coffin gives 1 to 3 Vampires
Coffin  Each coffin gives 4 or 5 Skeleton Archers
Dragonfly Eggs  Each egg gives 2 to 5 Fire Dragonflies
Snake Eggs  Each egg gives 2 or 3 Snakes
Spider's Egg  Each egg gives 2 or 3 Cave Spiders
Thorn Sprouts  Each thorn sprout gives 5 to 8 ThornHunters
Only one random number is created per use of the items, no matter how many items you specify. So if you specify to use 100 Dragonfly Eggs, for instance, you will get 200, 300, 400, or 500 Fire Dragonflies.
