This makes Bruxish a strong basic card to have on your bench, ready to deal a final blow to high HP cards
Apex Avian even negates by sending itself back to your hand, meaning that you can summon it all over again to do it again and again and again and again, creating a whole host of problems for your opponent
Sure, your opponent gets too as well, but if youre dropping a creature with an exceptionally powerful enter the battlefield trigger, like Atraxa, Grand Unifier, a creature that is practically unstoppable like Emrakul, the Aeons Torn, or an enchantment that gives you free rein to do whatever you like Omniscience, you basically guaranteed a win
3 mana for a 1/1 with Double Strike is rough, and the Phase effect is cool, but also costly