Boomerang was added in Eon Production's 7th expansion.
You have the power to return. Whenever you are the defensive player, you immediately challenge the offensive player first, anywhere on his home system. All rules for a normal challenge apply. After your challenge is completed, the other player's challenge resumes.
Wild Flare - Whenever any of your tokens should be lost to the Warp, you may keep them. (Return them to bases if necessary.)
Super Flare - After completing your Boomerang challenge, play passes to the left of the player who was about to challenge you.
Not long after popping, baby Boomerangs learn to toss twigs, shards of bark, even dried fruit peels (if properly shaped) in widening circles of flight. As they ripen this develops into an all-consuming game. When fully mature, they cannot resist the example of all the heavens and sally forth into happy orbits, barely perturbed by the presence of others.
The power description seems unclear as to whether the Boomerang gets a second challenge if his first is successful. Logically, the answer would be "no".
In its essence, the Boomerang's power simply means that he has more offensive challenges than other players, so it bears resemblance to the Machine. Of course the manner in which he achieves the challenges is different.