Green Prototypes is a rare construct unit that has the downside of giving strength to an enemy unit on death. The strength of Green Prototypes can be increased by leveling it up. Green Prototypes works well in aggro and sometimes, construct decks.
Green Prototypes' cheap cost and 1 movement make it great for pushing your front forward.
Since Green Prototypes gives strength to an enemy unit on death, you can play it in a way so that there are no nearby enemies nearby when it dies.
Green Prototypes can be used to advance your front 1 tile for 1 mana, which is very cheap. Expanding your front can have many benefits, like giving you more space or to move up an attack.