Space Gun

On its own this is a middling early magic gun that empties your mana bar in a few seconds. Wearing a full set of meteor armor, it costs nothing to fire, and at a stage of the game where mana is the only thing limiting a mage, unlimited shots from a fast weapon matter more than any raw damage upgrade you could make instead. Treat the gun and the armor as one item. Picking up the gun without the set is barely worth the detour.

The lasers grow as they fly. A shot that has crossed a room hits harder and punches through more enemies than one fired at point blank range, which inverts the usual instinct to close in. Hold a sightline down a corridor or across an arena and let the beams do their work on the way to the target. The growth stops well short of the maximum range, so you do not need to be absurdly far away, just not standing on top of the thing you are shooting.

Meteorite normally means waiting on a meteorite to fall, which usually means killing something first. There is a shortcut. Gold Chests down at the bottom of the world, close to the underworld, draw from the same pool as shadow chests, and that pool includes Meteorite Bars. Open every gold chest you pass on the way down and you can be firing this before you have beaten anything at all.

Against a single target it holds its own with the Thunder Zapper and often does better, and with the set bonus behind it, it stays your main magic option through the whole first half of a world. The Laser Rifle is where it stops being the answer. Reforge to Mythical if you intend to keep it that long, though note that the mana saving on that modifier is dead weight while the set bonus is active. What you are buying is the speed and the knockback.