Collectible Card Game Headquarters

This is most probably not doable, but you never know if you don't ask.

In DoTP 2012 - there was free for all, 2 headed giant, archenemy mode
In DotP 2013 - there was free for all, 2 headed giant and planechase mode
In DoTP 2014 - there was free for all, 2 headed giant and also sealed deck play.

What would be great is if wizards could save all these different modes of play for subsequent DoTP releases. I would even pay extra money for a DLC that does this. Because I got in at DotP 2013 I never played archenemy mode, until I recently downloaded DoTP 2012 with DLC allowing me to play as the archenemy.

Is it possible for say create an archenemy mode for a different version of DotP or are the versions code too different?

Possible, yes. Likely, absolutely not.

It is possible to reverse engineer both the Lua code and the engine, but most (if not all) of us lack the skills to do so (not to mention reverse engineering is technically illegal). Putting the Archenemy mode in would require getting the Lua source for at least parts of the interface, changing what is probably a relatively small part of the engine, and putting in the appropriate layouts, graphics, and scheme cards to support it. The easiest parts would probably be the scheme cards and graphics. It may be possible to adapt the layouts from 2012. However, we still likely won't be able to decompile the Lua scripts required or make any changes to the engine.