Well, I was going to post a priority user, but it's not necessary anymore, I see. Many suggestions are great, so I'm going to give my opinions, before suggesting something new.
Breloom is brilliant, carries Spore, scares out Terrakion and Kyurem and hits hard basically anything. The only concern I have is that it cannot set up SD safely on nothing, since it's OHKOd by, respectively, Psychic from Meloetta, HP Ice from Thundurus, Ice Beam from Kyurem and CC from Terrakion (Metagross threatens to 2HKO with any move not named Pursuit, and since you don't OHKO with +2 Mach Punch you must Spore it before attempting SD). This means you must rely on prediction to set up your SD, while the Scizor set posted is much better at gathering boosts. However, Breloom retains key advantages in more immediate power available, Spore and a resistance to Water - which seems extremely valuable if they pick Choice Scarf Politoed as their last pick (although it still takes over 70% from it, and with LO recoil it can mean an OHKO regardless).
Scizor is again a wonderful suggestion. Both Bulky SD and Band have their own advantages.
Band is perfect to scout, dealing over 40% to Metagross and Thundurus with U-Turn (so the Steel-resists are worn down quickly), has plenty of power readily available, and completes the infamous, archetypical VoltTurn core with Scarf Rotom-W. However, the fact that they can exploit a Choice locked Bullet Punch in many ways (Metagross, Thundurus gets a "free" switch-in, and an eventual Choice Scarf Politoed can do the same, and threaten to OHKO with Hydro Pump) can be a letdown. Also, if we want to pick a set-up sweeper, we would have only one slot left, so we would be hard pressed to find something that isn't ruined too hard by Terrakion, has decent type synergy with our team and performs good against their team. THis is not too much of a concern, but still something to be considered.
Bulky SD from alexwolf is very interesting, and probably one of my favorite entry so far. It just needs a bit of damage on the Steel resists, and can easily dismantle their team with +2 Bullet Punches. Roost means easy set-up on Kyurem, so I won't dismiss it easily; however, U-Turn is very useful in my opinion to weaken common switch ins and for general scouting. I once ran a SD | Roost | BP | U-Turn set that performed quite well, I'm not sure it's appropriate here since it means you have to switch out after a SD if Metagross is still up (although it would be a free switch in for Rotom, so not that bad anyway), but it can be an idea nonetheless.
Scizor also leaves us weak to a few pokemon- ScarfNape immediately becomes a huge problem, with CC OHKO'ing Tran and Mamo, Flare Blitz/Overheat OHKO'ing Scizor and Celebi, and both doing a considerable amount to Rotom. Magnezone becomes quite a problem too, Volt Switching all over our faces, HP Firing Celebi and Scizor, and Flash Cannoning Mamo switch ins. We can counter either, but only one- meaning team 1 will get a pretty big advantage, depending on which one we choose. Gliscor/Skarmory to counter Nape won't work at all, because Thundurus/Meloetta just plow right through them (Kyurem as well, for Gliscor) Bulky waters won't work either, as it can easily run Grass Knot, or again switch to Meloetta/Thundurus to eliminate. For Magnezone, a fighting type could handle it- but don't forget that they have a base 128 special attacker in the wings. Strong priority, as well. Lucario is an option, but that leaves up horrendously weak to Nape. I know this is a lot of planning ahead, but we're almost at the end of this teambuilding- so we have to watch out, because we don't get the last pick.
There have been some very valid points raised in regards to whether or not choosing Scizor would benefit the team more, or open team 2 up to a serious threat. However Alexwolf is entirely correct in saying that we can use the 6th slot on team 2 to counter on of the listed threats to Scizor and the rest of the team (ScarfNape & Magnezone). While it is obvious that we do not wan't to waste our last slot countering only one member of team 1 so that the 5th pick can be a little safer, I believe there are plenty of options that can serve to both cover the 5th member and limit team 1's choices. After all that is the aim of this thread.
There are a few reasons why I like Scizor over Breloom; we all know that Breloom is indeed a powerhouse and access to a 100% sleep move is really very nice, however lets be honest, it can't take hits. The set Electrolyte posted in particular, with only 4 HP evs and LO racking up quickly isn't really going to do it any favours. While in no way is it an undesirable set I honestly think that the pick could be used better. Granted the one thing which Breloom will sufficiently handle better is a Scarftoed if team 1 decides to go for that, because as previously mentioned BP isn't really doing anything, while Mach punch is a OHKO. However thats just one situation versus many more, and I don't believe the scales add up in Breloom's favour in this particular situation. Either the Scizor set I posted, or the one Alexwolf posted could be used for different reason. Both have their advantages, and disadvantages.
The set Alex posted well have an easier time sweeping without a doubt, as it will not be locked into one move, and as he explained there are more than ample situations in where it can easily get to +4 and sweep. That set compliments Celebi quite well as now there would be a set-up sweeper from both the special and physical side of the spectrum, both who would be serious threats after one or two boosts. The set Alex posted also has substantially more bulk than the CB set, which is needed to ensure those safe boosts, that coupled with access to roost means that it is likely to be a lot more durable than the CB set. The only real disadvantages with the set, looking at the current situation is that if somehow Scizor only has one turn to attack, and it
really needs to grab the KO with BP or U-Turn and it just misses out on Ko'ing, it could potentially leave team 2 open to a serious threat. This is more a hypothetical situation in regards to team 1's final pick. Or potentially if Scizor has to come in while Thundurus is at +2 where Focus Blast (if it hits, which of course it won't) is a guaranteed OHKO (111.37-131.19%). Even if Thundurus has come in twice as well as firing off an attack, leaving it to be at ~40% HP, BP off the bat isn't dealing anymore than 30%, allowing Thundurus to KO with the FB and still have enough HP for 1-2 more attacks, depending on whether it had already fired off an attack. Of course it's a very similar situation for CB Scizor, however it can comfortably deal over 35%, with a chance to hit 40% straight up, which would mean that in the same scenario Thundurus dies and Scizor is still around to do what it does best.
Ganj4 made a good point in saying that by running CB we lock ourselves into a move allowing team 1 to temporarily gain the upper hand in any given situation, that is why I generally tend to avoid running Choice items on my teams, bar Scarfs on things that can easily switch out (e.g. Rotom). However for the current situation, given where things stand, I feel that the immediate power that a banded U-Turn or BP does is quite essential. I don't really feel the need to say this as I know I am far from the most experiences player to have posted on this thread, however team building, and this team in particular, isn't about picking pokes that can beat each and every member of the other team single handed. That is why I believe that checking, and threatening 4/5 of the current members on team 1 is really quite impressive. The fifth threat being Metagross who does not appreciate a U-Turn, and isn't really all that threatening to Sciz himself. It is true that the CB set will require more prediction, but I honestly think that whoever ends up using this team will be more than adequately equipped with sufficient prediction skills. That said, the main idea behind this CB Scizor on this team, is that the only two attacks which really ned to be used are BP and U-Turn. Pursuit might be nice for Meloetta-A, and Superpower for Meloetta-P, however really its only the two aforementioned attacks which will be used primarily.
CB Scizor isn't meant to stay in for more than a turn or two in the early stages of the game while things such as Metagross and team 1's final pick are still around and healthy, so just constantly U-Turning around, dealing a lot of damage each time, is the main way to go. BP is there more for mid to late game cleaning, or early game if you wish to immediately eliminate, say Kyurem or Terrakion. That links to what I said before about a teams overall cohesion, and when you have that so well known VoltTurn core, maintaining the upper hand early-mid game shouldn't be too difficult. While I understand that in the early stages up until now really, it was evident that team 1 was packing the harder hitters, and that the main strategy there would be to apply offensive pressure from the start and never let up. However the VoltTurn core can counter that quite nicely. While it may be fairly obvious where the next switch is coming from, an unexpected switch can take away all of team 1's momentum, and put team 2 on the front foot.
Electrolyte was entirely correct in his/her future predictions and reasoning as to what team 1 could pick in their final slot, however there is time for a more detailed analysis of
all the picks which team 1 could use to counter Scizor and other members of the team, which is why I really like what Alexwolf said in regards to picking our 6th member to support both Sciz and the rest of the team. I think right now picking Scizor opens us up to a
few specific threats, however the amount of pressure it puts on team 1 far outweighs any of those, and if we are intelligent about how we analyse exactly which pokes would then be threats to team 2, we can pick the 6th member accordingly.
All up I think Scizor is the best of the pokes submitted so far, and not to be narcissistic but I think CB is better. I posted the CB set before Alex, over a set similar to Alex's because I did a similar analysis in my head and found that it really seemed a lot better for the team. The role of CB Scizor is to punch holes and keep momentum, while Alex's set is to sweep. I feel we have enough sweeping potential as is, and in a possible late game situation even CB Sciz could sweep with BP.