I agree with skarmory and chansey dropping, they are too much "set up fodders", today's metagame isn't by any means kind to them, especially skarmory, we have seen a rise in usage from magnezone after aegi's ban.
I think Slowbro as A is a bit too much though, he just as skarmory and chansey isn't that threatening, and while he's a great help in stopping things like excadrill and keldeo it's not very easy to fit in a team.
Manaphy cannot break stall without external help by a knock off user or don't know something like gothitelle in order to kill chansey, and it's too slow to do something against offensive teams, especially if we consider
thundurus who can easily kill him, but it's not only that, latios is for example another problem for it especially if manaphy lacks psychic, together with venusaur if lacking psychic, ferrothorn if lacking hp fire (umm wait what)
assault vest azumarill is also an acceptable check for it, while keldeo can 2hko him with secret sword, while he can resist a +0 psychic
Of course they are cute sets like cm+rain dance+rest, but that only gives you scald as an offensive option, and this kind of manaphy is even slower than the "common" one.
Long Story SHort: too slow against offense, has trouble breaking stall, 4MSS
And yes, I also vouch for Mega Dactyl, and Megazam, especially Aerodactyl, i'm sold on this thing after watching some Frontier's replay, a great "bird" check, coupled with recovery, taunt, sky high speed? Yes pelase!
The only downside is the fact that he takes a mega slot, but oh well.
mAlakazam has been already discussed but yeah, modest is the way to go, you still surpass stuff like Greninja without problems and get more power from timid orb alakazam.
And really, trace MIGHT be situational, depending on the occasion, but here we have Keldeo an S ranked pokemon with an useless ability, ability does not make up the entire pokemon, and stillt race can still be useful against stuff like
magic guard clefable, poison heal gliscor, flash fire heatran, sand rush exca, intimidate landorus-t, sheer force landorus-i prankster thundurus (if you have substitute, that is) protean greninja (fairy type alakazam? Yes please) multiscale dragonite and so on.
About crawdaunt:
These Pokemon have more notable flaws than those above them that affect how they function in the tier. Their positive traits still outshine their negatives, but they require a bit more team support to bring out their full potential.
Yeah, crawdaunt has flaws, but can still be mitigated with proper team support ex: trick room support and it's a force to be reckoned with b- for me.
Eh, I dunno about Hydreigon, haven't used him much so I'll leave it at that.
Cresselia is also b- rank material imo, while she's a great wall, she's not limited only to that, access to trick room, great bulk, and lunar dance, a better version of healing wish mind you, makes her a great trick room candidate, if not one of the best.
As for thundurus, it's uuh, quite a "mega slot" case, I mean, if you use thundurus-therian, you can't use thundurus-incarnate, you know.
lower speed also doesn't help him that much, you might say that being immune to electric type attacks is kind of a great deal, but as far as I'm concerned they are only three "serious" electric 'mon in the tier:
Rotom-wash, Thundurus-Incarnate and Mega Manectric, you can't stop manectric, thundurus might get the best out of you with knock off/hp ice, and hydro pump really hurts you, so yeah, a bad niche, perhaps he might be useful against zapdos, but eeh.
I'll make a case for Jellicent, though, for D rank (c- is kinda suicide, you see)
While it's true that jellicent is setup fodder for quite a big deal of stuff so is stuff like mantine, tentacruel and blissey
What jellicent brings to the table? The same stuff Mantine does without being SR Weak, and I guess resist some weak volt switch from rotom-wash, combined with wow which got a major accuracy boost from bw, taunt along with immunity to scald makes him an okay stall breaker.
Of course, that does not mean that jellicent is capable to walk on stall teams, stuff like venusaur, charizard x and amoonguss can give him trouble, but it's still something to consider when we rank him, pdef jellicent, the old standard from bw can also win the 1 on one against excadrill, or to be more precise
he has an 85% chance to win the "battle" which means that jellicent can come in on excadrill's rapid spin, rock slide or iron ehad and scare him off with wow, even with stealth rocks and sandstorm on the field, he also has some chances against starmie, which gained a bit of usage after the aegislash ban, all in all, I believe that Jellicent fully deserves D Rank