REDU format ruling
Assault Mercenary

Nearest-era rulings (Tengu, Sept 2011) — no REDU-specific archive exists.
Card effect (current official text)Once per turn, you can return 1 "Assault Mode Activate" from your hand or Graveyard to the Deck to destroy 1 Spell or Trap Card your opponent controls.
Rulings
(1) Once per turn, you can return 1 Assault Mode Activate from your hand or GY to the Deck to destroy 1 Spell or Trap Card your opponent controls.
- The (1) Ignition Effect activates & resolves on the field.
- Returning the "Assault Mode Activate" to the Deck is a cost.
- This effect targets the Spell or Trap Card you wish to destroy.
- If you return "Assault Mode Activate" from your hand to the Deck, reveal it to your opponent.
Rulings data courtesy of Format Library — formatlibrary.com. Spotted an inaccuracy? Flag it in the REDU forum — sourced change requests get reviewed.