Ancient Amuletor (HP)

Summoners first appear on 2-1 and are the wizards wearing the blackdark blue robes. If you let them live long enough they will create summoning portals which allow other enemies to bypass crystals or otherwise traverse the map in a fashion that is out of the ordinary. These portals are stone arches with a purple vortex inside. Simply destroy 50 of these portals to get the trophy. A good place to farm is on 2-1.