Super Demo World is basically the first major SMW hack ever released, and to this day it remains one of the biggest. It remains an impressive achievement, although it has flaws; the difficulty curve is absurdly erratic and there are some rather annoying quirks (for instance, you can lock yourself out of one of the secret worlds or prevent yourself from getting some secret exits if you don't know what you're doing). I don't know who thought the world four castle was a good idea, but they were wrong. Regardless, this run is pretty consistently entertaining to watch and it's fun to see how thoroughly the speedrunners broke some of the levels.
The Second Reality Project Reloaded is one of the best hacks for the game and deserves a TAS to match. Unfortunately, this one isn't it; it doesn't clear all the levels and the runner has an annoying habit of flying over/under the stages (which is faster, but makes for a less entertaining run). A run has yet to be made that adequately shows off everything in this hack. I'm not sure one ever will, but I live in hope. Regardless, this is a pretty well optimised run that gives you a vague idea of what the hack is like, but I'd rather have a 100% run. I'm hoping its sequel, which is equally well made, will get a 100% run at some point as well.
And now the ridiculous Kaizo-style stuff
Kaizo Mario World 1 & 2 (see first post for Kaizo Mario World 3):
Present Mario (I haven't watched this one yet, will comment later):
Mario Must Die (I can't remember if I've watched the whole thing of this or not but it's pretty impressive):
Cool or Cruel:
Super Mario Tabarnak (note that this run isn't particularly optimised, but it's still entertaining enough to watch):
Springboard and Shells Hack (yes, silly name, but the hack itself is quite impressive):
Item Abuse 1 & 2:
Glitch Abuse 1 & 2:
ColonThree:
Pit of Despair:
Pit of Death:
Pit of Keys:
Living on the Edge:
Wall Jump Abuse:
Hard Relay Mario (two different playthroughs):
Falling Mario:
Falling Mario Brothers (not sure if this is the same hack creator as the above, but it has a number of similarities):
Super Mario Forever (aka Super Mario Frustration):
Super Mario Air 1 & 2 (note that Air 2 differs from the original mainly in that invisible coin blocks are marked and the player can no longer perform infinite jumps; also, the Air 2 run is aiming to show as much of the hack as possible rather than for fastest completion, which explains a number of differences in the routes taken):
And finally the infamous SMB-inspired Syobon Action (aka Cat Mario or Dongs.exe)
I like how some of these have more re-records than frames