@Zappergeck said:

What if an alternative order has gaps? E.g. series 04 of Ridiculousness: On http://www.mtv.de/shows/x7gvgx/ridiculousness-S4 there is a list of episodes from 1 to 20, lacking number 15.

Is it possible to map this into an order list? But I can't find any possibility to leave an episode number unset.

It is not possible to leave a gap in an episode group. So, in that case, you will have to put the epîsodes 16 to 20 as episodes 15 to 19.

Btw, possibly related or not: what is it about these kind of "play"- and "skip"-like buttons right under those order lists? What do they do - I can't see any effect when simply trying...

They are pagination buttons. If the list is too long, it will be divided in multiple pages.

Thanks for this immediate reply, I already doubted that there would be a solution.

The pagination buttons seem quite obvious now - I probably hoped too hard that there could be a hidden possibility for that gap problem to see the simple function... :-)