This effect is probably the most situational in the game, and one of the most powerful.
Strategies and game play:
Power options that make you offline cards from your hand, like Change-up or digimon that allow you to offline them for effects work great with this. I like it because it makes such cards, which would otherwise be awful, actually useful. You can either send your control spire card offline with even steven, or by purposefully losing the duel.
Combos with other cards:
You're probably going to need to use resist downgrade to keep your digimon on the duel zone after sending so many cards from your hand offline. Even steven is essential to reliably set this off.
Ways to counteract it:
The best way to counteract this is to either save an option eater, or to have beezlemon in your deck.
Skipping digivolve levels is insanely powerful.
Again, this card is HIGHLY situational.
I give this card a 7/10. It would get a 5/10 for its hit or miss playability, but its cool-factor/fun factor gives it the extra 2 points for me.