1) Aegislash @ Leftovers
Ability: Stance Change
EVs: 252 Def / 252 Sp Def / 4 HP
Moves:
King's Shield
Shadow Claw / Shadow Sneak
Iron Head
Sacred Sword
Relaxed Nature
2) With Thick Fat, Mamoswine might be a great Pokemon in my team, although I see an inconsistency in your moveset, and Mamoswine isn't a Pokemon that should learn Special moves because the high Attack stat will be wasted if you do so.
3) Whenever there is rain, there is Heliolisk. Its Ability and moves are just perfect for destroying Rain Teams and Kyogre. Heliolisk's Dry Skin works pretty well because rain also helps it to use Thunder effectively. Grass Knot is a surprise attack for Ground (and even Water/Ground) Pokemon. They will never think that my Heliolisk learned Grass Knot. While Toxicroak's Dry Skin helps it recover health in the rain, it can't really make use of the rain since it has no moves that is boosted in the rain. I was thinking about Surf, too, because it's boosted in the rain, but since Water/Ground Pokemon are common in competitive battles, Grass Knot is a better choice. Heliolisk can also be used in conjunction with Lapras' Rain Dance.
4) My Crobat isn't for 1-on-1 battle, that's why the Attack stat needn't to be so high, and it doesn't need to learn strong moves. Crobat is the main annoyer of the team. Therefore, the Speed stat should be as high as possible. My Crobat has so many use: First, status giver: Confuse enemies, Poison Fang them until they get badly poisoned, then leave. Second, Baton Pass destroyer with Haze. Third, Belly Drum and Swords Dance destroyer with Confuse Ray or Haze. The reasons why I don't just use Toxic instead of Poison Fang are Magic Bounce and Taunt, though the latter is rarely used against Crobat. Super Fang might be a nice addition to annoy Steel Pokemon even more. I'll consider adding it.
5) You have no idea how many times my Lapras and Altaria have been status'd: About 6 to 9 out of 10 battles! Rain teams are uncommon, that's why I taught Lapras Rain Dance. Also, Rain Teams are uncommon, but Pranksters are not.
1. Aegislash benefits more from offensive-boosting natures than defensive ones. Aegislash's EVs carry over between forms; for example, Aegislash's Blade forme can't benefit much from the Shield forme's Defense EVs, as it's very frail; this is why Aegislash has EVs invested in an offensive stat of choice so it can hit harder in Blade forme. Shadow Sneak is needed on Aegislash to give it revenge killing ability:
-Iron Head/Shadow Claw
-Shadow Sneak
-Sacred Sword
-King's Shield/Swords Dance
Nature: Brave/Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Life Orb/Weakness Policy
2. Despite its inferior Special Attack, Mamoswine is a fine user of Freeze-Dry; it's Mamoswine's most reliable option against Wash Rotom; Freeze-Dry also does more to Slowbro than Earthquake would. That, and the other users of Freeze-Dry (Aurorus, Delibird, Articuno, non-Mega Glalie, and even Lapras itself) aren't viable in my eyes. Don't believe me? See the calcs:
16 SpA Life Orb Mamoswine Freeze-Dry vs. 248 HP / 0 SpD Rotom-W: 143-172 (47.1 - 56.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
16 SpA Life Orb Mamoswine Freeze-Dry vs. 252 HP / 24 SpD Slowbro: 174-211 (44.1 - 53.5%) -- 87.5% chance to 2HKO after Stealth Rock and Leftovers recovery
252 Atk Life Orb Mamoswine Earthquake vs. 252 HP / 232+ Def Slowbro: 146-173 (37 - 43.9%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
Yes, the Freeze-Dry attacks only 2HKOs, but hitting these Pokemon on the switch is key here.
3. If you really, really, hate status, I highly suggest you give Mega Altaria Refresh or Heal Bell. The former gets rid of status problems for Altaria itself, but has more PP, allowing you to stall out Toxic or Will-o-Wisp, while the latter cures the party of all status problems, but has less PP, meaning you have to be conservative when using it. In Heal Bell's case, you have to know when to heal and when to set up/attack. If Mega Altaria is faster than the opponent, it can also use Substitute to block an incoming Toxic, Will-o-Wisp, or Thunder Wave, then set up with Dragon Dance as the opponent switches. On another note, Manaphy is a better Hydration abuser because of mono-Water not having a lot of common weaknesses.
4. True, Toxicroak doesn't have access to Water moves, but it's still an effective user of Dry Skin. It doesn't matter if a Pokemon can't fully benefit from an ability or not as long as it can use it in some shape or form.
5. The Crobat set I posted is more consistent for these reasons. On another note, it never had any Attack EVs in the first place; please look more carefully at it:
-It can prevent opponents from setting up with Taunt (which also addresses the Baton Pass problem, as Baton Pass is a status move), followed by statusing them with Toxic (which always poisons the target, as from Gen VI onward, Toxic never misses when used by Poison Pokemon; remember that Magic Bouncing Toxic isn't much of an issue for Crobat, as it's immune to the Poison status condition) or whittling walls down with Super Fang, which has a higher impact than "annoying" them with Confuse Ray, which I don't recommend for the below reason.
-Confusion is an unreliable status ailment, as it's easily cured by switching out.
-Crobat has a stronger STAB option in Brave Bird or itemless Acrobatics if it has to attack. If you're using Super Fang, a common tactic is to use Super Fang on walls until they're within the KO range of either move.
-Poison Fang is very weak and doesn't poison all the time. A 100% chance to poison with Toxic is better than a 50/50 with Poison Fang. Similarly, Aerial Ace is also a rather weak attack unless it's being used by Mega Aerodactyl, whose Tough Claws ability boosts its power to acceptable levels.
-It has a reliable recovery move in Roost, allowing Crobat to remain in the game longer. The general rule of thumb in competitive battling is if a defensive/support Pokemon has access to a reliable recovery move, such as Recover and Roost, that move is mandatory. Most Pokemon can learn Rest, a full-heal recovery move, but it's not a reliable recovery move because it forces the user to sleep for 2 turns (unless the user is using Sleep Talk, a move not every Pokemon can use effectively).
While Crobat is hard-countered by Mega Sableye, remember that you have other teammates to deal with it.
If you hate Magic Bouncing Pokemon that much (the premier ones are Mega Sableye and Mega Diancie), I highly suggest you follow up with the Mega Altaria suggestions, for the reasons I already stated. Mega Altaria hits Mega Sableye super effectively with Pixelated attacks. While it's true that Mega Diancie's Fairy STAB hits Mega Altaria super effectively, Mega Altaria can win if it manages to set up a Dragon Dance:
+1 252+ Atk Pixilate Mega Altaria Return vs. 0 HP / 0 Def Mega Diancie: 294-346 (121.9 - 143.5%) -- guaranteed OHKO
+1 0 Atk Pixilate Mega Altaria Return vs. 0 HP / 0 Def Mega Diancie: 214-253 (88.7 - 104.9%) -- 31.3% chance to OHKO (guaranteed after Stealth Rock)
On another note, you need a Stealth Rock setter on the team, as Stealth Rock helps get chip damage on opposing Pokemon to make KOing them easier. Refer to the Stealth Rock setters I posted for options.
If you're still not convinced about my arguments for Heal Bell/Refresh/Substitute and against Facade, here are quotes taken from Altaria's OU analysis. I have to admit, Substitute is rather prediction-reliant:
Originally Posted by Smogon
Refresh and Heal Bell are alternatives to warding off status, with the former having more PP, allowing it to last longer against persistant status users, while the latter has much less PP in exchange for the ability to support its teammates.
Originally Posted by Smogon
Substitute is a neat support move that protects Altaria from status as well as fatal attacks.
Originally Posted by Smogon
Substitute requires more prediction, as Altaria then can't switch directly into status, but it yields great results when used on the opponent's predicted switches. In such a situation, Altaria can choose to either set up or hit the switch-in with Return while behind a Substitute.
Originally Posted by Smogon
Facade can replace Return to take advantage of any status conditions Altaria has taken. However, it is greatly reliant on the opponent having status users in the first place, making it situational and somewhat contradictory with Heal Bell or Substitute.
Originally Posted by Smogon
Facade benefits from any status conditions Altaria might have taken and is absolutely usable on any set that utilizes Return. However, it is overall very situational, not to mention weak and almost useless if the opponent doesn't happen to have a status user at all.