Reveal a Space unit card from your hand to your opponent and put it into your build zone with 1 build counter on it. Play only during your build step.
Keywords
Stack
Stack: [List]: A layered, static ability that means "You may put a listed card under this unit as part of its stack." The listed cards can't be on top of the stack. Cards with the Stack ability don't count as the cards listed and don't contest with any of the listed cards. If a card is listed by its name you can't stack a card with a different name unless it satisfies a different criteria in the [list] or they represent the same unit. (See the "Different Versions with Different Names" section in the rules PDF) Unlike a normal stack, you can only have one version of each unique unit from the [list] in the stack. Non-unique cards listed on a card with the Stack ability are permitted to form a part of the stack and you can have multiple cards with the same name in the stack as long as they are non-unique. Cards added to a card's stack using the Stack ability cannot exceed the 4 card maximum normal stacking rule. If a unique card with the Stack ability has another version of itself move to the top of it's stack, discard any cards in the stack that can't stack with the new version on top of the stack.