Allows the user to pick from the mythic horns to be exchanged with the current horns on a dragon. 

Dragon's Blood rules: 

• Every level up a dragon gains an extra Dragon's blood slot (up to 4 total)
• Only one of each rarity may be present on a dragon (common, uncommon, rare, and mythic) 
• Only two markings may be added - rest must be other traits on the dragon (breath, skill, eye/horn, mutation, etc) 
• Old Dragon's blood from before this rule may not be grandfathered - they may be submitted as a caim to gain back the 5 Dragon Soul Coins used to purchase it instead.