This unit costs 1 fewer build counter to deploy if there is an Aquatic Location in the Ground arena.
Choose a unit in the Ground arena with health 4 or less and set it aside, along with its Pilot, if any. Play only when this unit would attack. When this unit is discarded from the Ground arena, return units set aside in this way to the Ground arena tapped.
The "unit" refers only to the cards in its stack, not Equipment. Simply put the Equipment in your build zone.
If the Sando is returned to your hand and not discarded, or if it's discarded from the build zone instead of the Ground arena, the set aside units would remain set aside for the rest of the game.