It doesn’t matter what it looks like before it’s mounted. It could be completely misshapen. Especially if the bead is not steel. Mount it on and see if it sits correctly once you inflate it.

I’d say that as long as the bead catches the rim all the way around, it should be fine. Assuming it’s still within the designed measurements, the rubber will settle in even and round out properly as you air it up.

It could prove to be a slight hassle at first, just start with very low tire pressure in the tube, just enough to put pressure on the tire all the way around, yet low enough that you can adjust and manipulate it by hand until it settles evenly and balanced on the rim.

I’d do that step with the rim mounted on the bike, so you can spin the tire and make sure it settles in evenly. Once you accomplish that, then go ahead and air it up to full pressure.

If after all that, you still can’t get the tire properly mounted, then send that shit back. But it can’t hurt to at least try, I got a feeling it’s probably fine.

I happen to have the EPlus variant of that Schwalbe Marathon, and when I received it, it looked in about the same condition. However, after mounting onto rims, checking that the bead seats properly, and then adding air, there was only minimal deviation when rotating the tire. And after a few laps on warm pavement and in the sun, the deviation was gone and it’s been perfectly fine for the past 9 months.

On a separate note, I’m not familiar with the term “mantle” for a bicycle tire, as a speaker of American English. Is that a regional term? Here in California, we call it the same as for an automobile: tire.