The missing ones in Ultimate Doom are E2M8 and E4M6, they are both "impossible" for the same reason: the Cyberdemon must be dead to exit the map, and there just aren't enough monsters (or powerful enough monsters) around to kill them.
For Doom 2, the missing ones --> map 2, which is extremely difficult but possible -- Sedlo made a TAS pacifist run in 0:31, and Adam W said he reached the blue key. It just takes lots of luck and lots of skill. Also missing are map 17, which is packed with hitscan monsters, tight passages, and lots of stuff to do (one of the longest speedruns in the IWADs) and topped off with an ending that is nearly impossible for pacifist play (again, it has been done with TAS), and map 26 which should be feasible (again, done with TAS)if you can somehow get to the red key (which I can't really see how you could get to in reasonable time -- i.e. before you get hit too much -- without killing the imps) without an absolute shitload of luck and skill, and get a little lucky with the Baron guarding the blue key. Map 30 hasn't been done but may be impossible by design, which is why it isn't even in the table.
Plutonia has two undone: map 30 (same reason as doom2 map 30), and map 7, where I can't really see how you could get out of the first area without shooting at least one Mancubus at least once (they will kill the chaingunner and zombiemen quickly, even if you can reduce the number of Mancubuses that way).
TNT has quite a few undone maps, most of those maps are prohibitively difficult for pacifist running. Some may be feasible (e.g. not more difficult than, say, p1m7 or p4m1), but TNT has generally attracted little speedrunning interest relative to the other IWADs. One of the undone TNT maps has been done with TAS by Xit.
Last edited by Kristian Ronge on 02-13-07 at 16:19