Place your carved pumpkins directly on top of the extended sticky pistons. Ensure the face of the pumpkin is looking outward so it looks like a normal patch. Crucially, the pumpkin is a solid block, so players/mobs walk on it. Place 1 piece of string underneath each pumpkin to prevent them from breaking accidentally when the piston retracts.
Replace the magma blocks with a 2x2 water flow that pushes victims into a central grindstone. This preserves XP orbs while maintaining the "patched" look above. lovely craft piston trap pumpkin patched