Sandcastle Bucket

Point it at sand and it drops a decorative castle, eating one block of sand each time. Every sand variant works, platforms included, and biome does not matter, so beach scenery can go anywhere you like. Four designs exist and the game picks one at random as the cursor moves, but the up and down keys cycle them directly instead of making you hover over block after block hunting for the shape you wanted.

The castles sit in the background layer and cannot be picked back up. A pickaxe deletes one outright, so lay the scene out before you commit rather than expecting to rearrange it later.