Contract with Guile

Whenever you use the spell True Polymorph to become a dragon, you maintain all spellcasting features and abilities from your spellcasting class(es), but when you personally come to possess any amount of coin (copper, silver, electrum, gold, and platinum), half of it is magically transported to Sardior's hoard for his services. In addition, you must offer a worthy magic item of rare or greater quality once per calendar year from the day you sign this contract.