Meteor Staff

You do not aim at the enemy, you aim at the ground beneath it. Meteors spawn high overhead and fall toward the cursor, so terrain between you and the target is irrelevant as long as there is room above the impact point. Underground it still works, because the projectiles pass through blocks for the first stretch of the drop, but a low ceiling directly over the target eats them.

This is one of the hungriest weapons in the game for what it gives back. Without a deep mana pool, regeneration potions and something like the Mana Flower, you will spend more of a boss fight recovering than firing. Work that out before you commit to it, not halfway through the fight.

Lock On does not help. The meteors follow the cursor no matter what the game thinks you are targeting, so aim by hand. On the other hand they throw off enormous light, and a few casts down a dark corridor reveal more of the map than a handful of torches would.