You can bundle custom props with your map by making a Model with the PrimaryPart set and putting it in the CustomProps folder.
ObsidianOrb🔗MapKit comes with an example custom prop for you to start off with: ObsidianOrb. This prop is basically a Bowling Ball, with the same tags and attributes. There are a few special things to note:
ObsidianOrb.PrimaryPart is set to the hitbox part of the modelObsidianOrb.Part has special tags: CanRideRail, Interactable, Explodable, PhysicsProp, and RollingFriction, all of which must be used on a BasePart and are used frequently across Blast Zone props.ObsidianOrb configure the behavior for the tags it has: Projectile, Prop, and TimedDespawn