There are many ideas for enemies. Those enemies are designed to be exploited with Stop Time and react to player actions.
As example the parasitised moai has two parts: body and infected head by a parasite eye. This enemy will become a spinning death trap if only the body is destroyed, so the player should try aiming for its eye instead.
Another enemy is the fish ship: Those come in two variations, Fish Ship and Fish Ship Master.
They come in groups with many fish ships and one master, if the player kill the master ship first, all the smaller ones run. This doesn’t sound gamechanger, but if you take in account how the fruit drop works, where the last enemy killed from a group drop a fruit, then is relevant to kill the smaller ships first and the master last, because if one smaller run, the fruit dropped is lost. Now there are consequences of maintain the master ship alive, because this ship is the one who shoot bullets from the group.
These examples are presented in the Alpha, but there are many enemies with reactive behaviors through the game.