I wouldn't balance against that. I would not allow a PC to pull off a 100 shift ritual in the first place. Worst case scenario, somewhere around 50 shifts in, every single local major power would converge on your location to see who's throwing around stupid amounts of power and shut you down. But in practical terms, I wouldn't even let a PC try such a ritual in the first place.
Kill 5 people: Congrats, you are now an NPC warlock with too many lawbreaker powers. While there may be some game concepts where this would be acceptable ("Hey, lets play as evil monsters!"), those aren't the sorts of games I run. Such games would need other balancing factors, like attention from mortal authorities and/or wardens.
Kill 50 animals: I wouldn't let this work; at best you'd get just a few aspects, like "animal sacrifices", "too much blood", "hecatomb"; I wouldn't give just two shifts per animal.
Make ludicrous piles of declarations: Also wouldn't work; declarations are against whatever target number the GM thinks is reasonable, and after the first few, I'd start adding in stacking penalties. Or, better yet, as you start to declare how conditions are coincidentally just perfect for your uber-ritual, I'd start throwing compels at the aspects you've declared - as every other major power in the area wants to make use of the same conflux of energies you're declaring exists.
Spend 99 scenes doing nothing: If you've been gone for 99 scenes, you're not a player in my game anymore; that's over a year of real-time not playing.