The moment Greninja was given one single (physical!) coverage move, people started going into pure hysteria about it, resulting in one of the quickest ban in history.
The same people decided that having Volcanion begin its run in OU was a good idea, and haven't yet started to suspect test it.
Smogon everyone!
Now that I got that out of my system, I need to ask: what is the purpose of this team? Because while I can see it doing a great job of spinning a silly meme, and while it seems perfect for being slaughtered horribly by every team that carries a bulky SR setter and Volcanion (I.E. every single team on SD right now), I am having troubles to see how it deals with the part about, you know, winning.
Problems I see in order of appearance:
1) Latias is under a horrible amount of pressure. It checks every single Pokemon that is problematic for this team... But it does just that. It is basically a go out, tank, Roost, Defog, come back kind of deal. Which is all fine and dandy if the opponent's team carries ONE Pokemon that is problematic to you, as in, JUST Volcanion or JUST Tornadus-T or JUST Keleo (listing this over Gyarados because, well, how the hell is Gyarados giving you problems?). But if the opponent is running any two from this list at the same time (which nowadays means, Volcanion and another one), Latias will be switching in and out an awful lot, eventually getting its lefties knocked off and its pretty skin scorched by hot steam. That will wear you down fast, I tell you... And the set you gave her does her no favor, either. While I can kinda sorta understand the choice of HP fighting, it being your sole offensive move means that, while you are not a lot better at taking on prospective Pursuit trappers, you are also a lot worse at checking the things Latias is supposed to check. Sub CM Keldeo still exists, and once it has foiled your Toxic with Substitute, it will soon get to the point where you either give it a free turn by switching out, or you utterly fail to break the sub with your non-STAB, low-BP move. And then the little pony will wipe out your team, because Latias is your sole realistic out to it. So yeah, Latias is a good way of dealing with the Pokemon that give you grief, but she cannot do it alone.
2) Keldeo is good per se, but I see it having an issue with the synergy of the team, which I will explain in more details later on.
3) Magnezone is good, moving on.
4) My problem with CBTar is that Tyranitar does not NEED to lock itself into a move (and locking yourself into Pursuit essentially means, their next Pokemon is free to set up at its leisure) to Pursuit-trap people. Heck I remember running a set for Ttar that had no Atk investiments a while back, and it was still enough to kill the Latis with Pursuit. So yeah, consider Assault Vest over Choice Band, retaining the same EVs and moves. You will still have enough firepower to kill people, you will hve the luxury of choosing which move you want to use each turn, and between AV and Sand, you will have enough SpDef to tank any non-Focus Blast special move in existance, thus giving you a way of assisting Latias in her eternal struggle to sponge damage. Basically, right now Latias has to switch into any problematic move: with the change I am suggesting, Ttar could serve as an alternate switch-in for some threats (Mega Manectric, for starters), thus making it easier to keep Latias healthy.
5) Keldeo, Serperior, Pinsir: see, this is where you lost me. So, you have two sweepers who need to set up, albeit in different ways, in order to get going: one physical and one special. On top of that, you have an extra special sweeper (scarfed, at that) in Magnezone. What do you accomplish by adding a third special sweeper? What does it do to help the team win? What are the threats it can defeat, or at least cripple, that the rest of the team couldn't already handle? You have physical Fighting coverage on Pinsir (incidentally, consider Storm Throw over Close Combat: when you factor in the guaranteed critical it has the same damage output, but bypasses screens and doesn't debulk you), and between Magnezone and Serperior, you achieve a special coverage that makes Water absolutely irrelevant: Scald's burn chance doesn't justify, by itself, carrying a coverage option you simply don't need.
Wouldn't it be wiser to have a defensive Pokemon here, something that can switch into some of those nasty threats that give your grief? As dirty as I feel even suggesting it, Quagsire could be a good match for this team: the Unaware variant stops the Mega Gyarados you are (somehow) so afraid of, while the Water Absorb variant is a great out to Volcanion and enemy Keldeo... Which means you can switch Quag, and not Latias, into those: suddenly, the main problem of this team (Latias being under way too much pressure) is solved. Plus, Quag has so few viable moves that you can easily give it Toxic and make it the status spreader of your team, allowing you to run some much needed STAB move on Latias (Psyshock being the top option, for the aforementioned CM Keldeo which still exists).
TL;DR: Psyshock over Toxic on Latias, AV over CB on Ttar, and Quagsire over Keldeo.