Heat ray any good?

[Sour Cream]

Thinking of using it with my mage, also, is spectre armor good with it?

[Drag]

It can pierce more than a fe wtargets (I believe indefinitely) which makes it pretty useful for mobs. It's far from an endgame magic weapon, but it should help int he process of finding something more useful in the hardmode dungeon.

[Dr. McWeazel]

If you're planning on doing either of the two Moon Events, the Heat Ray is almost the perfect weapon for the first 3 waves (infinite piercing, decently high damage, low mana cost). The only things I've found that perform better in the first 3 waves are both melee weapons, and even they do so with at best dubious consistency.