Ok, so I was actually going to rate this when you first posted it and I never found the time to actually do it, so here goes nothing.
Tyranitar - I see that you want an offensive Tyranitar and while CB is great, I prefer Dragon Dance T-tar. You will want 252 Atk and 252 Speed with 4 Def. Have him hold an Expert Belt with the moves Ice Punch, Earthquake, Crunch, and Dragon Dance. Go with Jolly instead of Adamant, Tyranitar isn't super fast so he is going to need all the speed he can get. I have used this set faithfully and it has yet to let me down. Just watch out for Fighting types.
Gastrodon - If I am not mistaken that is the set I gave you (Credit to Devil's Advocate) so it makes sense that I have nothing to say other than how beastly this thing is.
Genesect - The set looks great but I think I have a way around your Nature problem. Remove his SAtk EVs and put 'em into Atk, then have him hold a Life Orb. His moves should be as following: Flame Charge, Shadow Claw, Iron Head, X-scissor. While I don't think this is quite as good as a special set, your nature pretty much kills off any chance of running a special set. Credit goes to Mew for that set btw.
Reuniclus - Not bad but I will be adjusting the EVs a bit. Run this spread instead (that rhymed), 252 HP, 176 Def, 82 SDef. Also, run Modest Nature. This balances out your defenses pretty well while giving you quite a lot of firepower at the same time. You can keep the Life Orb if you want but you might favor Leftovers instead, your call.
Mamoswine - There are 2 things we can do here, we can change Stone Edge for Stealth Rock (I might add that you NEED Stealth Rock) , or we can keep the set and give him a Choice Band to turn him into an offensive Powerhouse. Once more, your call.
Now this is where I start to have problems with the team, Chansey is draggin you down, and is nothing more than one more fighting weakness at this point. So depending on what you did with Mamoswine you will have 2 different replacements for Chansey.
If you chose to put Stealth Rock on Mamoswine, then congratulations, your 6th team member is now.... Landorus!
Landorus @ Choice Scarf
Trait: Sand Force
EVs: 252 Atk, 252 Spd, 4 HP
Earthquake gets boosted by Sand Force and serves as main STAB, while Stone Edge is coverage and is also boosted by his ability. U-turn allows him to gain momentum as well as revenge kill, while Superpower/Brick Break serves as coverage, Superpower has superior power but Brick Break does not lower your physcial stats.
If you chose to put a CB on Mamoswine your 6th team member is.... Jirachi!
Jirachi @ Leftovers
Trait: Serene Grace
EVs: 252 HP, 252 Spd, 4 SAtk
- Stealth Rock
- Charge Beam
Stealth Rock provides your hazards, Wish is for the recovery of Jirachi and the team, Charge Beam is coverage and raises you SAtk, while Psychic is STAB.
Good luck with the team!