This is a basic negative mold for casting Aria the Dragon, based off the model by loubie. I cast using Rose's Metal, a Bismuth/Tin/Lead alloy whose melting point is lower than the melting point of ABS and which has next to no expansion/contraction during heating/cooling. Thus, you can pour liquid Rose's Metal into the ABS mold and not have to worry about it melting the mold, or busting the mold open as it cools. Rose's Metal melts at 208F, which is low, but it can still burn you. You can use pure Acetone to help dissolve the mold off. HIPS plastic is another option for the mold, with d-Limonene or turpentine as solvents.
This mold doesn't have a separate vent chimney to displace air, so I had to tap the side of the mold with a screwdriver a lot to get all the trapped air out and metal into all the crevices of the mold where it needed to go.