Hovering your mouse cursor over a bubble will give a brief tooltip on the mechanics of that card. Clicking on a bubble will take you to the page about that card.
The gray box indicates cards that can be produced at a Stagnant Reservoir or Festering Corpse. Maggots are spawned each turn, and upgrades must be researched.
The black arrows indicate the tech requirements for each upgrade. For example, to research Suppression, you must first research Infection I.
Simple: To research Airborne Pathogen, you must first research Contagion I. You cannot begin researching Airborne Pathogen until Contagion I is finished.
Moderate: To Reanimate an enemy unit, you must research Infection I, then Suppression, then kill an enemy unit, then morph a Festering Corpse into the suppressed unit.
Advanced: There are several ways to create a Festering Corpse. One is to kill your own Abominations: First research Infection I. Then have a Mosquito attack a Maggot or another Mosquito, which will cause it to morph into an Abomination. Have the Mosquito attack that Abomination to give it a Carrier attachment. Once the Carrier card is face-up, kill the abomination with Infection I to turn it into a Festering Corpse.
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