In Apex Predator, all units have one of three combat classes: melee, ranged, or long range. The combat class and engagement of a unit affect what cards it is allowed to attack during the combat phase:
|Ready||Engaged once||Engaged twice||Engaged three times|
|Melee||Can attack any nearby card.||Can only attack other Melee units. Cannot attack Ranged, Long Range, or structures.||Cannot attack||Cannot attack|
|Ranged||Can attack any nearby card.||Can attack any nearby card.||Cannot attack||Cannot attack|
|Long Range||Can attack any nearby card, or any card in an adjacent location.||Can attack any nearby card.||Cannot attack||Cannot attack|
For example, if a Harvester is engaged once in the same location as an enemy Gulbar, a Barbed Agama, and a Temple of Ctenos, the Harvester can attack the Gulbar, but not the Agama (because it is ranged) nor the Temple (because it is a structure).
If a unit is bringing a new card into play, it cannot attack, regardless of its combat class or engagement. For examples, a Gulbar building a structure, a Rat building a siege weapon, a Harvester splitting, and a Mosquito morphing into an Abomination would all be ineligible to attack until those actions complete.