Obliteration 10, "Dirty Joke"
Save 16 of 20, SR 75 (Locked), no time limit
1 bomber, 7 builders, 5 stackers, 3 diggers
This is one of the last remaining stragglers among backroute-prone levels - and to be fair, that might be because this level was added much more recently than any other. The original Obliteration 10 had a backroute that seemed unfixable, so I replaced it with this as a new level. (That removed level later got put back, with the backroute intact, at an earlier position, since the tester who found the backroute mentioned that it was still pretty challenging to even find that. In place, a different level - probably the worst one in the pack - got removed.)
This is also the second-widest and second-largest level in Lemmings Plus Alpha, at 1016 pixels wide (x 240 tall), beaten by a level of 1296x200 (259,200 pixels total, vs 243,840 total for Dirty Joke). Both these levels fall well short on tallest level though, as one level is 400 pixels tall (though only 160 pixels wide). Despite the size, Dirty Joke's intended solution replay solves in under 3:30 - and I'm almost certain this could be brought under 3 minutes, and maybe even under 2:30, with some optimization.