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I meant move the projectiles up on the Z axis in a timeout loop when they're about to hit a wall tile-type that's excluded, then move it back down when it passes.

Alternatively, one could start the projectile with a Z value, then snap it to the floor when it hits a wall, unless that wall tile-type is excluded.

This is all assuming that you can even interact with projectiles after they're spawned. Otherwise, you could write your own projectile handler.