Porygon-Z is a nightmare to balance. I'm surprised we didn't just reserve it for ubers. It has nasty plot, download, and a bunch of nice coverage. Along with some moves that support it a liiiittle too much. It can recover.
Now, Reinitialize is an ability Hematite used for his mega klinklang submission and lemme tell you it was insane. Mans gave it- You know what. I'm not even gonna spoil it, go see it for yourself:
https://www.smogon.com/forums/threa...telle-conkeldurr.3666825/page-21#post-8591494
Anyways, it's basically a cop-out to balancing a pokemon. I-I mean its basically a cool and effective method of making a mon with overkill stats scale down to a manageable level. The trick is that this PZ can only use moves of the same type to attack and setup unless it hates stat changes. Nasty plot would have to be used beforehand, locking you into Tri attack temporarily.
So then I said "well PZ has conversion, so what if we made the ability more open ended?" If it decides to convert into lets say an Ice type from Ice beam, it can still use Growth before changing type, it just takes a bit of setup. However, it becomes a really powerful attacker WITHOUT setting up since its special attack is so high. With a speed tier like that, you could run webs just to outspeed anything that comes your way.
Some other cool tricks involve Solar Beam + Growth + Conversion under sun. Probably with Recover or Tri Attack so that your normal-type moves aren't useless. Thunderbolt + Conversion allows you to use moves like Thunder Wave without being punished.
Accupessure is a fun way to snowball before changing your type again. It's ludicrous special attack makes any form of speed buff or defense buff insane to counter, because now its actually capable of walling attacks, outspeeding pokemon, and hitting even harder if its lucky. You might save conversion for last with a move like ice beam to shred your opponent later.
Growth makes sense flavor-wise as computers and programs are always evolving, always changing, always growing..
Last but not least, Agility + Conversion can be abused with Psychic or Psyshock.
There are still options to explore, and I want YOU to go and search for them! that way this description's a little interactive and not just a giant block of text you quickly scanned through. Plus this would help you plan out sets if this submission happened to win!