I've found that celebi has been a big letdown for me in the past, and really has much more of a genesect problem than it's worth imo. Regenerator, while passively acting, has proven to be one of the most important facets of the team. Often times you don't find the time to use that healing move, so having a way to heal up automatically is a godsend.
I was planning to replace Gliscor with Specially Defensive Hippowdon, since in honestly gives the same stuff Gliscor does, minus a fighting resistance and ground immunity, for much extended bulk and ability to beat things like genesect and jirachi, things that really troubled me in the past. It also has a huge natural power for a stall team, which would be useful in wearing down things like reuniclus. What do you guys think?
EDIT: after some thinking, I can most definitely conclude that ditto is crap for a stall team. If you switch in to transform and kill something, then the only way to do that is to have the opponent be good against themselves...such as HP ice landorus. But, this means that they can nail you with it on the switch. Well, then, why not just wait until something goes down and revenge kill? Because that's the complete opposite of stall. In that case, the opponent can just switch out an bring their poke back in later to wreak more havoc. That's what I don't like about "sack something and revenge" pokemon...like kyurem-b. But I won't get into that here....at any rate, my most important thing to keep in mind is to keep the pokemon alive at all costs, which ditto goes against. The only way it would be useful would be transforming into an opponent's defensive pokemon (like a gastrodon that you've toxiced, assuming they don't have toxic themselves) and wall "yourself". Or transform into your opponents spinner or something. But relying on your opponent to spin away their own hazards? That's just bad strategy.