Another one that's best shown visually. In NeoLemmix,
steel is steel - it cannot be destroyed under any circumstances (this is one of the
things I love about NeoLemmix).
Note in this NeoLemmix example that 2 Bombers have been used to create the first crater in the platform, and the second has been created by a Digger. Both craters show destruction right up to the edge of the steel, and it's necessary to use a Climber to exit the digger pit:
By contrast, performing the same actions in SuperLemmini produces a completely different result. The second Bomber has blown a crater in the steel, whilst the Digger was stopped several pixels short of where the edge of the steel is, meaning that the lemmings can simply walk straight out of the digger pit:
Similarly, in this level it's possible to dig and bash through the edge of the steel in SuperLemmini, provided some part of the skill path is in contact with a substantial enough amount of terrain (this means that 100% is possible in
Compression Method 1):
Whereas, in NeoLemmix, this is not possible:
I prefer NeoLemmix steel to be honest; it makes more sense and is far more predictable. But, the more oddly-behaved "classic steel" in SuperLemmini means that alternative solutions may be possible.
Please note, this steel behaviour in SuperLemmini can be disabled from the 1.43 Editor, and the steel areas can be resized independently to fit the blocks exactly, so that SuperLemmini steel behaves exactly like it does in NeoLemmix. This means that levels can be edited so that the steel differences are nonexistent, however since NeoLemmix does not allow classic steel behaviour
at all, it can be considered a fundamental difference between the two engines (albeit one which can be manually tweaked user-side). Furthermore, since SuperLemmini "(un)officially" presents the original games with classic steel enabled, this is how the levels are intended to be played in that engine, and challenge rules normally state that levels cannot be edited anyway.