I just noticed this over the weekend, and don't have any real details. I got two Polymorph cards and both were marked, No PVP. If this is on all of the new cards, I think it's a real improvement for PvP for the lower levels. I also noticed that my older Polymorph cards, do not have the No PvP mark on them. So it's only the new card, or maybe just the new drops, I'm not sure.
Joseph. Joseph LionHunter, Balance, Storm, and (a non pvp ice).
You probably got the actual treasure card for it instead of the bought ones. I think the reason they do this because correct me if i'm wrong i think you can trade crafted, and treasure card pack polymorphs. But they make it so you can't PvP with them.
I've only seen the no pvp symbol on the draconian polymorph so far, but then again that may be the only one i got recently. i have tons of poly tc's from celestia that don't have it, though. they just say no auction, i think. i've never tried trading them, though i don't have any real use for them besides the treant one. -eli and crew