Hi everybody!

So, I want to make a 2D multiplayer game in MonoGame (or XNA without Live) and I'm desperately looking for an open-source C# 2D side-scroller engine that supports multiplayer. I don't need very much, only the bare-bones engine with the network part already done, I'll code the rest.

I also considered the idea to make one by myself, but it's too complicated yet for me, especially the networking part.

Could anyone suggest me some engines that match my requirements?

Thank you in advance for your support!

open-source C# 2D side-scroller engine that supports multiplayer. I don't need very much

That is actually a considerable amount.

Trying to get "the networking part" to stay in sync is a very important part of the design, and any changes you implement will probably require adjustments to it.

Accommodating for lag and other network considerations is a significant effort, any added or changed features might end up trickling down into significant changes to the network code, often with slightly different results on the sender and the receiver.

You might start by going through the list of games on SourceForge, perhaps reviewing the listing at http://sourceforge.net/directory/games/sidescrolling/ to find something similar to what you want.