Streamline

Streamline does a decent amount of damage, especially when upgraded. It can be difficult to play the first time, but then becomes extremely energy efficient as it gets cheaper. Hologram allows you to pull it on a nonthreatening turn for its initial cast, or pull it when already discounted as a cheap source of damage. Can even eventually be pulled by all for one. I typically take one copy in act one if I'm low on damage against elites or the boss.