Just a hunch, but try going to the library and check for a side quest. Don't know the name of the quest, but when you finish it you get badge Bookworm. Basically you go around Wizard City to all the bosses and fight them again to read the book.
Don't worry too much, that minion is pretty good at hitting Feint with Dark Sprite, or, casting Vampire at that Feint when its a full health and you are about to die. Oh yeah and then the monster hits you with that trap on yourself. I'm trying to say the minion is as dumb as a box of nails. At least its not like the Life Minion before the Celestia update, she would heal herself endlessly until the moment you put a Life Trap on the monster then she would hit it. The Death minion might have its uses against Death Shield spamming Life monsters, but a Death Wand, Poison and the Level 58 Skeletal Dragon give you pretty good coverage on that issue, or just put some Ghouls in the deck, and then you can use them to finish a battle.
I used Animate for the Level 48 quest when I could not get a Prism to show up. Which ever one does Storm Shark. Watch out, Minion #8 can cast Doom and Gloom, so you better not be relying on Sprite or Pixie to heal (you shouldn't at that level anyways, you should be the master of Death Blade, Death Trap, Curse, Feint, Prism if you need it, and Wraith).
Some time later I noticed you can get Death Prism Treasure Cards at the Bazaar.