Form is a card type that is unique to the Beetles. There are 4 forms:

Forms allow beetles (usually Harvesters) to morph into the specified unit.

To bring a form into play, choose a Thinker to which you will assign the form. If that Thinker is already supporting a form or upgrade, discard it. Place the new form face-down underneath the Thinker, then engage both cards 2 turns.

If a form card is discarded or a Thinker supporting a form is destroyed, all units of that form must immediately revert into a Harvester or die.