If this card is destroyed then you can special summon 2 Phantom Knights monsters from your graveyard with the same level, then increase their levels by 1
This makes it particularly valuable against hand traps that disrupt combos
If it's a Pendulum Summoning deck, there won't be many monsters in the Graveyard, so it's easy to Special Summon even in the middle of a duel
The novel idea Brian and his team (Aaron Forsythe, Mark Gottlieb, Matt Place, Paul Sottosanti, and Henry Stern) had was to use self-milling as an additional cost
More than being a very cost effective way to draw spells it is a rare example of card draw outside of blue or black which gives a lot more options for building and designing decks
The card back designs were in the Expedition, Aquapolis, and Skyridge expansion sets