Meteor Head

The Meteor Head is a flying enemy that spawns in Meteorite crash sites. They often spawn in small groups around Meteorite ore. They will continue to spawn as long as over 20 blocks of the meteorite ore is still there.

They have a chance of dropping meteorite ore themselves, so if you go near a meteor you can just keep killing the meteor heads to get an endless amount of meteorite ore. They also drop the most coins upon dying. Proven false

Mining Meteorite ore can be quite difficult as these enemies tend to attack relentlessly, giving you no time to mine. The best possible way to do this, however, is to use a Pickaxe for Mining and Fighting and the same time (make sure the Meteor Heads are all on one side, face them, then start mining - they also get hit by your pickaxe, resulting in rather undisturbed meteorite mining).

Some weapons (most notably Flails and boomerangs, although in my testing phaseblades will also inflict substatial knockback) upon impact with the Meteor Head can send them flying quite a distance, thus giving you some time to mine the ore.

(on a side-note, if you have a Fiery Greatsword, it knocks them allmost off-screen, giving you more then enough time to mine)