A terraian, with break only choose skill. Example. Basher can't bash wall, with wall dig only digger.
NeoLemmix and SuperLemmix (and Lix?) aleady have one-way arrows for horizontal-only and vertical-only destruction, in both directions. The only thing that's missing is Bomber-proof/Bomber-only terrain. We could look at discussing that idea and see if people think it's worth adding to SuperLemmix.
1-Just add the button in editor level speed, or (and) lock fast forward button in editor
Yes, adding it as a level design feature is most likely the way to go. However it could also be implemented as a global option that the player can toggle on and off at any time, so that
any level could be a "superlemming-speed" level at the push of a button. Then, it would likely be added to individual levels as an optional "play in superlemming mode" Talisman. We could even do both.
As for 2-player mode, the first thing I want to try is lemming "tribes," so that each lemming tribe can have it own dedicated exit that other lems can't access. If I can manage that, the next step will be to allow the tribes to access any exit, but count towards the saves for whichever tribe the exit is for.
In the meantime though, I'm taking a bit of a break from adding new features for a while. The most recent version of SuperLemmix was only released yesterday, and I've already found a handful a bugs that will need to be fixed. I'm going to concentrate on making levels for a little while, and testing the existing features as extensively as possible, before adding anything else.