Put the Tank set as the first set, as it is probably its best set due to its high bulk and even higher special attack. Also add an Agility set as well with Agility / Thunderbolt / Dragon Pulse / Focus Blast as it has a bit of niche, allowing it to counter Tyranitar after an agility boost and most notably outspeed Thundurus, which can't hurt much with HP Ice (252 SpA EVs have a 59 percent chance to OHKO)
Overview
Extremely slow* and mention how it becomes slower after Mega Evolving
"Obviously a mega in team overview" and "Takes up mega slot" should be gotten rid of and you should mention how it gains a mega evolution as one of the first things or else it won't make sense when you say "Dual STAB"
Mention how Mold Breaker isn't amazing but it allows Mega Ampharos to hit Thundurus-I, so mention that
Rest Talk
Whimsicott doesn't have an analysis as far as I know so be cautious about that, you may want to cut it out.
If you're giving Focus Blast a mention, consider slashing it on the set.
Talk about why a Modest nature is necessary.
You should rename this set to "Specially Defensive"
Tank
Put this in front of the Rest Talk set
Take about how Discharge is a usable move because of its high paralysis chance, because I don't see that anywhere.
Talk about why a Modest nature is necessary.
OO
Take agility out and make it a set, it can work really well imo outspeeding Tyranitar and Charizard X which would otherwise OHKO. Make this the last set as it is the one with the smallest niche out of the three.
Talk about Thunder Wave and Toxic and how a stall set can be effective (Cotton Guard, too)
I scanned through this and this is what I found. This is my
UU Analysis which may not help too much, but you can use it for reference if you want :)
This was made on December 20 2013 and has 0 checks, I can take over if needed/wanted (I'm not sure if the OP is still looking at this) as I have no OU analyses going on.
Thanks
TheManlyLadybug for tagging me, hoped I helped :)))
EDIT: Just realized it was agreed that rest talk was better before the tank set, sorry.