Hydra Cave/1.03

Plaguelords
Caskets are available to the Plaguelords in tier 3 and they are needed to allow Spores to be produced at the Temple of Eyes. Caskets are small and somewhat weak for a building, but they cost quite a lot of both gold and crystal. Fortunately, you'll only ever need to build one (assuming the enemy don't get their hands on it) so the price is really only a one time expense. Other than allowing Spores to be produced, it can also research damage upgrades for them. Each of these upgrades only offers a minor damage improvement but yet cost a sickening amount! It is indeed believable that the game could be over before you get the final upgrade.