The mirror options sounds really nice!
These are some game mechanics that I personally prefer, as well as things to look out for when programming the game; (Probably some people will disagree with me on some of these)
-when selecting lemmings have worker/walker/left right priority options
-when selecting certain lemmings; example: when trying to make a lemming a climber, have priority on non-climbers. I say this because in Lemmini and sometimes other programs as well it seems difficult to select the lemming I want, that is; it keeps highlighting the lemming that’s already a climber.
-Bashers and miners don’t turn around when they hit steel.
-if a lemming is standing partly on air, (like a digger on the edge) he can’t be made a blocker and thus fall.
I’d recommend you go over these big glitch lists just to familiarize yourself with the sort of thing that’s happened in Lemming games past and to look out for. A lot of these things come about as natural consequences of the game mechanics. But you probably already knew this.
http://www.lemmingsforums.com/index.php?topic=525.0http://www.lemmingsforums.com/index.php?topic=693.0-------------
some other suggestions:
-highlighted Lemmings turn a different color when the cursor goes over them. This makes it much easier to see exactly which lemming is being selected.
-the option to select a lemming first then click a skill to assign it instantly (the reverse of the normal behavior), like in Clones. Though I'd definitely want this as an option and not mandatory. Having both of these modes would, I think, be an awesome advantage to the game. Clones being only the one way makes it really jarring to play for the first time.
-another thing I just thought of: consider having numbers like the timer turn color when it's getting close to zero or making noises even. This would be especially helpful on multi-player games (even if your not doing anything multi-player) I like lots of funny noises in my games
-have all the stats of a level displayed somewhere while the level is playing
-“break apart” this is a radical and highly involved idea I thought of a while ago that entails being able to highlight a group of tightly cramped lemmings and zooming in and having them separate out temporarily, making it easy to select a specific lemming. This is probably my least useful idea.
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as far as new game elements like downward one-way-walls, everything I had is pretty much in that topic. Some I like more than others. Some are taken directly from L2 and Lemmings Revolution.
My favorites are:
level entrances are separate entities.
exits with a max limit of how many Lemmings can go in.
disappearing terrain
pre-placed Lemmings; uncontrollable lemmings
doors and switches
moving traps like weasels
gravity pads
I personally don’t care for more than the 8 regular skills.