To feed your dragon a crystal, approach its head and talk to it.
Crystal Effects
Example Effect: Terra Crystal
In the image above, you’ll see a Wind Dragon that has not been fed any Terra Crystals. The Wind Dragon starts with a 4×4 Farm Plot. In the next image, you’ll see that it becomes a 5×5 Farm Plot after the Wind Dragon has been fed Terra Crystals once.
Where To Get Crystals
Method 1: Monsters via Spell Seal
Use your Spell Seal on monsters to get a chance to obtain Crystal Fragments. Most monsters in dungeons drop predominantly the same type of Crystal Fragment. Once you’ve obtained at least 5 of the same Crystal Fragments from monsters, it’s time to trade them for a complete one at Crystalabra. Every Crystal requires 5 of its fragments to be traded for a complete one. And you can only trade crystal fragments with Heinz. Note: In the morning, Heinz roams around town. He goes back to Crystalabra in the afternoon at around 2:30 PM.
Method 2: Buying Crystals at Crystalabra
Crystals can be bought at Crystalabra for 50,000G. Tip: Crystals will be 45,000G on Fridays thanks to the 10% Discount Sale. Crystals become available once you’ve done the 1st renovation for Crystalabra.
Method 3: Encountered in the Overworld
When you’re exploring Rigbarth, its surrounding areas, and dungeons, you’ll often come across complete Crystals. Keep your eye out for them and you’re bound to find some in unlikely places. Tip: Use your Charged Spell Seal to get inaccessible Crystals