Official art for Buck: Legacy card game, illustrated by Secret-Pony, depicting a Pony Spellcaster wearing the Crown of the Black Lily, a Treasure card which appears in the Buck: Legacy core set.
The symbol of the Fleur-de-lis (called the Black Lily in Buck: Legacy) is the sigil of Loria, and one of great power and significance. This ancient artefact significantly increases the wearer's magical ranged attack power.
Fun fact! Like many illustrations in the core set, it's design loosely resembles an item from Dark Souls, in this case, the Crown of Dark Sun Gwyndolin.