Under combos are what are revealed when Link pushes a pushable block.
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[*]File->New
[*]Place combo #624 somewhere near the middle of screen 0x00 (you can pick whatever combo number you want, but this is a block)
[*]Click the skull triangle flag icon in the Screen Panel; the Select Combo Flag window should open
[*]Select Push Block (Vertical, Trigger) and click OK; the mouse cursor should now have a flag next to it
[*]Click the combo #624 you placed on the screen - you should see a flag number "1" appear in the top-left of the tile as the rest of the tile turns blue
[*]press ESC - you should see the flag number and blueness disappear as combo #624's block image reappears
[*]Screen->Under Combos - the "Under Combo (Layer 0)" window should appear
[*]Click the block icon to the right of "New"
[*]select combo #948 and click 'Done' - this crystal ball is what will be revealed when Link pushes the block
[*]Click 'Set' in the "Under Combo (Layer 0)" window; it will be dismissed
[*]Quest->Test, save the quest as a .qst file, and then click 'Test' in the Test Quest window
[*]In zplayer, walk Link over to the block combo and push the block from the south
[*]Observe the crystal ball is revealed as the Zelda unlock chime plays
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If the under combo is not setup (like if you skipped steps #7-#10) then a black square will be revealed when Link pushes the block instead.