Ok I'm gonna try again. First off I agree that gengar and sleep are annoying but they really didn't benefit or get hurt from any new mechanics in gen 7 and both were manageable in gen 6 so i don't see the need for immediate action (sleep might of gotten better with most walls running vest instead of goggles + weakening of PH but that's beside the point.)
I honestly don't think belly drum/shell smash were anywhere near bannable in gen 6. Let me go over what changed.
1) Mons get full evs. I've heard that this "weakens" shell smash but anyone with any brains can see it really doesn't. If something can't tank power trip, it isn't gonna tank it after 252 evs. defense evs aren't gonna stop 1000 atk. they just aren't. If something CAN tank it, it would already have 252 evs in hp and defense anyway probably. But because the shell smash/belly drum mon has 252 evs, extreme speed/other priority usually does a pitiful amount of damage, almost always <50%. That means u can't really revenge kill it.
2) Priority Attacks is weakened. This happened in several different ways. First, gale wings was nerfed. For me that means no more d-ascent, which could normally take out 90% on most mons. This leaves espeed. As you guys know, ate was nerfed from gen 6 and mons have more defense, and the damage usually isn't sufficient to kill. I've seen damage as low as 30% taken on an espeed. not even enough to kill drummers. In addition, priority has a general bad time of it because of new abilities like queenly majesty phazing them out and making them far less common. So basically this check, which SINGLEHANDEDLY put smash in its place in gen 6, doesn't really exist.
3) Prankster was nerfed. This means no more encore on dark types. That REALLY HURTS. that was another of my go-to stops for setup in gen 6. Even without spectral thief/haze the extra turns were still enough to let me get around the threat. well that doesn't really work anymore. D-Bond was nerfed. As someone who doesn't use d-bond too much I'm not at liberty to say much here, except I imagine it can be annoying, especially without the threat of encore looming. Topsy turvy can't manage stuff anymore. This is pretty big. Topsy turvy was a big hit to setup and you can't really use it anymore because of targeting. And because you can't put any pressure at all on smashers they are free to batter away at you till they stall recover/ outpredict your switch and smash= u lose another mon. So you have to stay in to keep the "threat" of haze alive while your opponent either kills you or they switch and the momentum goes to the opponent.
4) Unaware isn't actually that good. People seem to think unaware is some magic answer but it really isn't. First off smashers are usually powerful enough to 2 hit or 3 hit (2 hit especially if it's a subpar wall like gyarados) So switching in often ISN'T an option. That means you lose 1 more mon. This is especially true if there is either hazards up, or your wall has taken ANY previous damage. It's important to note that without any passive healing it's almost impossible to maintain a wall at 100% (you can't run leftovers because spore) so you really have to run multiple walls. One for actually walling stuff, and one for stopping stuff like shell smash. Along with the fact that these walls have pretty short lifespans in general, there are new moves like sunsteel and moongeist to give them grief. This rules out notable walls such as Tina, audino, and solgaleo, and reduces many to subpar options like gyarados. To really hammer in just how bad this is, this is damage calc of a popular belly drum set vs gyarados.
252+ Atk Groudon-Primal Bonemerang (2 hits) vs. 252 HP / 252+ Def Gyarados-Mega: 156-186 (39.5 - 47.2%) -- approx. 32.8% chance to 2HKO after Stealth Rock
So, Gyarados canț switch in which means often an even 1-1 trade. Even with preparation you still are 1-1. Thats friggin terrible. pdon has now broken even through no demonstration of skill on 1 move. If you make the asinine assumption that you can switch in because everyone knows that its super easy to keep weak ass walls like gyara at 100%, there is still the chance that its running bolt strike. Yes groudon has a lot of attack, but everything that smashes has around 170+ anyway so i don't see it as a big factor. Yes bonemerang is unresisted, but these mons tend to have 3 coverage moves, it isn't hard to find a unresisting move. It's true that this is a stab move but lots of potential drummers (mmx/ray/etc) have stab unresisted and mmx has super effective stab (byi gyara). Also it's important to take in account that bonemerang is by no means some 150 power base move. It has 100 BP, and that isn't that powerful. Lots of moves have the capability to do more than that. This is my most important point: It is important to rmember that this is actually a pokemon battle, not a damage calculator were everything starts off at 100% and stays that way. It is so so so so so so so so so so so easy to deal 20% to a mon in a battle and have it go unhealed. Remember u-turn is super effective. I am tired of people telling me to run gyarados on the grounds that it theoretically checks shell smash. What I'm trying to say is that unaware doesn't work because it's a bad ability that doesn't do much to strengthen a mons ability to switch in/heal, it's a bad ability because two very common moves check it, and it's a bad ability because the niche answers (gyarados) that people purport can stop shell smash really can't. And even if it could check it, you have to stay in to heal while the momentum goes to the opponent
5) Chansey didn't really get nerfed in any big way but it is very difficult to beat smashers because some have unburden and you usually have to sacrifice a mon anyway to get chansey in. Also, because of defense debuffs, many can outdamage or kill chansey anyway. In my opinion, chansey is just worth more than smashers and I don't regard that as a very even trade. So basically when looking at chansey, you're often looking at best a 1-1 +heavy damage on one of your most valuble mons and at worst a 6 mon sweep.
6) Innards Out is banned. God rest it's soul.
Because I know you guys like hard examples ima give u some.
Player A has a MMX and Player B has team made to defeat smash and a regen Zygarde out at 20%
MMX uses simple shell smash and zygarde switches to fur coat tina
MMX uses stored power
Tina dies
Regi switches in and hazes
Regi dies to close combat.
MMX has taken 0 damage and killed 2 mons. Its sash is unbroken.
lets imagine that they switched into a different check to MMX, something you would never normally do if you donț already know mmx is simple. That mon is unaware zygarde. Now usually with smash teams, terrain is usually up
252 SpA Mewtwo-Mega-X Stored Power (260 BP) vs. 252 HP / 252 SpD Unaware Zygarde-Complete in Psychic Terrain: 589-694 (92.6 - 109.1%) -- 56.3% chance to OHKO
zygarde is in all probability dead given the difficulty of keeping mons at 100%.
Ok kids! that didnt work so lets try gyarados. That will work for sure!
252+ Atk Mewtwo-Mega-X Close Combat vs. 242 HP / 252+ Def Gyarados-Mega: 390-462 (99.7 - 118.1%) -- 93.8% chance to OHKO
Rip gyarados is dead now.
How about chansey?
+4 252- SpA Mewtwo-Mega-X Stored Power (260 BP) vs. -2 252 HP / 252 SpD Mewtwo-Mega-X in Psychic Terrain: 3079-3624 (431.2 - 507.5%) -- guaranteed OHKO
Today is not ur lucky day. Rip chansey (yes i made it the correct HP, but i did ignore eviolite cuz at 500% who cares) even if chan wins the speed tie it dies cuz sash!
You send out aerilate Ray, but since psychic terrain is gay and terrain extender exists, ray is now an endangered species
Notice I have taken 1 mon. Matched it up against ALMOST EVERY SINGLE COUNTER NAMED and won with 3! moves.
That is one mon. The team built specifically for checking Bullshit is now gone because of ONE switch. Talk about a stakeout that continues until everything is dead.
Lets imagine regi has destiny bond and i know that.
Regi used destiny bond!
Mewtwo X used Encore!
rip regi.
Even if regi uses haze, he still dies to subsequent close combats.
I know this is a hypothetical situation but I have seen the mon described used under conditions similar to this with the same basic results.
So to conclude, every possible check to smash/drum has been crippled and this has created a perfect storm in which a centralizing move can be slapped on to most anything and can still be expected to win. Smash comes with no warning, and is not perdictable. Before the ev limit was lifted it was possible to spectral every deoxys you saw and get away with it, but now we have spectral dealing ~20% to possible smashers and that is just not enough to put any pressure on them, especially since these prospective smashers have 3 attacking moves to choose from while they batter away at you. Any of the ways I listed for dealing with smashers either ends up in your mon dead or momentum going to the opponent (except for chansey) how is that ok? Basically, it's far too hard to deal with, and we shouldn't have to deal with it anyway. Thanks for your time and please please please ban shell smash and/or belly drum.