[Opponent's Turn][Once Per Turn] When an opponent plays a Digimon, by revealing 1 card of the same level in your hand, place that card on top of your security stack face down.
Rulings Q&A — 3 entries
Q1Q3463
Is the card placed on top of my security stack by this card’s effect the Digimon played by my opponent or the card revealed from my hand?
You can activate the effect, but you can't add cards to your security stack, therefore the revealed card can't be added to your security stack and is trashed by the rules.
No, you can't.[EX2-045 Calumon] is a card with no level, so it isn't considered to have the same level even though it's the same card, and you can't use this card's effect to reveal it.
