damn your right I got a new computer and lost track of my files, finding the movie will take a while
this is in text version more of less, as you can read it is not a definitive plan (ie what special to use or how to get the exp for gastly to trigger L100, its wrong on the post):
http://speeddemosarchive.com/forum/index.php/topic,8457.msg235192.html#msg235192
Too bad on the box using the party counter instead of the FF marker.
About the poison, the poison doesn't crash the game, the 99s that are inserted at the status value byte at least. As you can tell since when you keep your party within its boundaries nothing happens.
What I mean is that the FF marks the end of party, sure its gone, but the next FF then becomes the new end of party, the item list's "end of item list" is the next FF. My assumption is that for step poison your party has more than 6 slots now. In other words the algorithm for step poison doesn't use the party counter but just keeps going until it finds the end of party.
It also means that after each step the game will check each pokemon in your party of more than 6 for poison status. The first ones have poison but also have a lot of life, but once you get out of your first 6 normal slots you start meddling with the pokedex and items regions first and then with other game data, if one of them is read as having a status of poison then their supposed hp would be reduced but since it is not actually hp and actually is something else that may or may not like being changed then the game crashes, in this case it allows one step but at the second it crashes, hanzou's allowed 10 I think.
You can check this by doing the bad ZZAZZ with 6 pokemon then manually restoring the FF, except one byte after its original place (making your party have 7 pokemon). That way your party will be longer but it wont get out the pokedex region. If you can walk as much as you want then my assumption is correct (although it would also depend on your pokedex data so make sure it is safe when read as a pokemon).
Just read your edit, cool, Im more interested on your interest of desciphering how this all works tho :P Specially if the info can allow to finish a run withot a special of 254, 254 requires an extra battle to raise evs.