Physical cards and dimension ripper...

[Padawan Pete]

I dont see how its a non issue. Can you not think of examples where knowing which card to retreat is advantageous to your position?

[kentuequi]

Put a thin sticker in the top right corner of your cards, then hide all the top right corner of every cards (yours and your opponent's), when you retreat a card, look at whose the card is...

[abazigal]

For me, the easiest solution would be to simply have a gentleman's agreement that such cards are set aside rather than put into the player's hand. This way, they don't get mixed up, and sorting them out is easier at the end of the game.

Sure, one player will be at a small disadvantage, but hey, it's just a game. Why risk friendships and all over such a minor technicality?

[Lime Street Hero]

Or simply exchange the use of "owner" to "controller" (ie the player who put the card on the field) and Bob's your uncle. That negates the advantage of knowing (by sleeve color or stickers or whatever) but the sleeve can still identify the card as yours at the end of the game.

From a game mechanics point of view, there is really no point in mixing physical ownership into the rules. Replace the wording to "caster", "controller" or whatever suits you.

[Inithra]

It would be harder than you think since the guy could say he has a jasmine in his hand and he didnt cast your one, while he doesnt have any (you cant see his cards). To be honest the physical cards are more just for collectors rather than trying to play the game. I mean its so much easier to just play against each other using 2 ipads or something rather than getting the cards out and fighting over rules for the whole day.

What the? Yeah, iPads are popular, but really? Are they an item every kid just owns these days? I'm an adult with a job and I haven't managed to scrape together enough for one yet, neither have many of the people I know.
Deck Protectors are, as has been said many times, the easiest and most cost effective way of keeping track of whose cards are whose.
There really aren't that many other rules that you'd need to keep track of. Health of each creature (counters/dice) health of each player (same), shadow crystals (same), durability (same...) and exhausted/frozen creatures (tap)