Big things might, sure, but that's not necessarily what we were talking about here.  Honestly, it really depends on what you're going for.

For a different perspective, a reasonable big thing catch might be +1: Radiation, and other penetrating effects where being bigger just exposes you to more of the effect.  (This is +1 on the assumption that wizards - a reasonably large category of supernatural individuals - could probably pull of some sort of relevant evocation if they knew the catch.  If you cut the catch down to just radiation, that'd probably be a +0.)
Or it might be +2 to +4: Any area effect attack - hunting mammoths with spears kinda sucks; hunting mammoths with grenades or maybe ballistae or by dropping really big rocks on their heads from a clifftop, on the other hand...

I could see deciding that were-creatures just have more "vitality" than other things and that the stuff-that-attacks-lifeforce catch isn't appropriate for them, though.  However, once you're dealing with supernatural vitality, then, imo, you're probably also dealing with something with a more traditional supernatural catch - silver, or the like.

Depends what the GM is going for, really.

So, did anyone else open up this thread expecting to see a discussion of what would happen if the wild hunt ran down an aircraft carrier - and the captain and crew decided to join the hunt?

...On topic, looks like a reasonable template & neat character concept.  Aspects are a good way of modelling slow changes and restrictions; if and only if you have a high discipline, then demonic co-pilot could be a good addition to the character, with the possibility of taking consequences like "What happened to my thumbs?".  (I've had one character with that power; worked out fairly well for her... but discipline was also her apex skill.  Not that that helped when she started slinging around demonic-co-pilot-empowered sponsored magic, but hey.)

Okay, the thing I'm not seeing in your example is why the "double were form" is in the same category as "general shapeshifter"?

Could you supply some more details?  Specifically, how did your player get a link to the fae lord in question?

Link?  Why would he need a link to them, when he can just cast a ritual to put a whole pile of aspects on himself?  Or use the ritual as a skill roll substitute to allow him to make a single devastating attack?  Or, etc.

The problem with the if I could do it so can they approach for thaumaturgy it is pretty much rocks fall everyone dies, its like saying stop using wail of the banshee and decimating all my opposition before the rest of the party gets a chance to act or I will have someone do the same to you. Which if you follow through becomes "yer I totally wiped out all of my PCs in one spell".   

Well, not quite - the fae lord would've had far more fun throwing a geas at the PC than just dropping rocks on him.  And there were plenty of opportunities to be sneaky about things, or call in allies of his own, or etc - I would've had no problem with the PC coming out ahead in the conflict; just that - like a fight between Harry and Cowl - it wasn't going to happen by application of raw power.

In this case, given the extreme limitations involved - you're missing most of the benefits of Inhuman Strength* - I'd suggest simply not taking the power, and having an extra fate point or two available to invoke your high concept for appropriate bonuses.

* I assume it is inhuman you're talking about, since that's the one that costs -2 refresh normally.  Supernatural strength normally costs -4; if your party is letting you have it for -2, that's already plenty of discount, in my not-so-humble opinion.

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.

I dunno about you, but I like to spread out aspects to be applicable to different things--after all, a character should be about more than just what they do in a fight.

Oh, absolutely - but, by the same token, each individual aspect should *also* be usable in multiple situations.  Sure, if your aspects are "boxing gloves of doom" and "sharp left hook" and the like, that's poor design - that should all be one aspect.  But you might have "mighty boxer" (taggable as how you fight) and a trouble aspect of "heart of gold" (why you fight) and, say "horror film nut" (for being able to fight calmly against an obvious monster like a RCV, or for trying ridiculous stunts with a "well, it worked in the movies!" quip) - that's three very different aspects, two of them mostly non-combat, all of which can be - in some circumstances - tagged for straight up combat bonuses.

And what exactly is your problem with Killer Blow? +3 stacked on top of whatever other damage bonuses you have (like Lethal Weapon or a Strength power) seems like a pretty alright deal to me.

The problem with Killer Blow is that, in most circumstances, you're better off not taking the stunt.  With the stunt, you can spend a fate point for +3 shifts on a hit.  Without the stunt, you can spend a fate point for +2 accuracy - and then, because you have one fewer stunts, spend another fate point for another +2 accuracy, for a total of +4 accuracy instead of +3 weapon rating.  (Now, you can contrive circumstances where it's better to have it than not, generally involving large piles of fate points and limited available aspects to tag.  But it's usually a bad choice.)