I think Minccino is very frail and despite I try with and Adamant nature (not Jolly) and Choice Scarf
There is no reason to run adamant minccino. It only gives you a 6.3% chance to do 1 more damage on your moves that are not tail slap. It's not advisable to use anything by life orb on minccino in my opinion. It stands out enough to be in C but being a powerful wall breaker.
Alright before I start, let it be noted that multihitting moves have their drawbacks like accuracy, flamebody hax, normal dmg resistances, and ferro barbs. These alone turn people away from these type of skill link attackers.
Here is an example attacking a 16 defense eviolite wall:
196 Atk Life Orb Minccino Tail Slap (5 hits) vs. 212 HP / 196+ Def Eviolite Spritzee: 20-25 (74 - 92.5%) -- approx. 6.3% chance to OHKO after Stealth Rock
(4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5)
Here is some example unrelated to aipom and minccino to give you an idea of how strong this is.
228+ Atk Life Orb Huge Power Bunnelby Return vs. 212 HP / 196+ Def Eviolite Spritzee: 17-21 (62.9 - 77.7%) -- guaranteed 2HKO
(17, 17, 17, 17, 17, 17, 19, 19, 19, 19, 19, 19, 19, 19, 19, 21)
196 Atk Life Orb Hustle Darumaka Flare Blitz vs. 212 HP / 196+ Def Eviolite Spritzee: 19-23 (70.3 - 85.1%) -- guaranteed 2HKO
(19, 19, 19, 19, 19, 19, 19, 21, 21, 21, 21, 21, 21, 21, 21, 23)
Note that the damage on tail slap does not increase again until 10 defense. Also it does not decrease from 4 damage hits until 20 defense such as koffing where they are only 1 damage attacks.
The only time adamant nature could truly be important to mincinno is when it is hitting something neutrally with 20+ defense. Here is an example.
196 Atk Life Orb Minccino Tail Slap (5 hits) vs. 36 HP / 236+ Def Eviolite Koffing: 5-20 (23.8 - 95.2%) -- approx. 12.1% chance to 2HKO
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4)
196+ Atk Life Orb Minccino Tail Slap (5 hits) vs. 36 HP / 236+ Def Eviolite Koffing: 20-25 (95.2 - 119%) -- approx. 6.3% chance to OHKO
(4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5)
Aipom does basically the same damage as mincinno however on targets with 16 defense it must be adamant nature to do reliable damage with furry swipes.
196 Atk Life Orb Fury Swipes (5 hits) vs. 212 HP / 196+ Def Eviolite Spritzee: 5-20 (18.5 - 74%) -- approx. 0.4% chance to 2HKO
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4)
196+ Atk Life Orb Aipom Fury Swipes (5 hits) vs. 212 HP / 196+ Def Eviolite Spritzee: 20-25 (74 - 92.5%) -- guaranteed 2HKO
(4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5)
For a last comparison here is adament LO aipom hitting a 20 defense koffing with fury swipes:
196+ Atk Life Orb Aipom Fury Swipes (5 hits) vs. 36 HP / 236+ Def Eviolite Koffing: 5-20 (23.8 - 95.2%) -- approx. 12.1% chance to 2HKO
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4)
As you can see Aipom can't actually simulate the damage of minccino on a 16 defense target without running an adament nature. Also mincinno completely out matches aipom when it comes to hitting a 20+ defense target. However a target with 20 defense that takes nuetral damage from normal types like koffing is really uncommon. I think the only other nuetral target with that kind of defense would be shellder but who in the world runs physically defense shellder? Spritzee and vullaby are 2 of the few walls that even bother getting 16 defense. Many other walls only use 14 defense.
I did find one last area of interested. On resisted hits mincinno has potential to do more damage than aipom on targets without eviolite. I'll use scarf/berry juice magnemite as an example. It would the same for noneviolite pawniards. With eviolite or anything over 16 defense resisted hits will always hit for 1's.
196+ Atk Life Orb Aipom Fury Swipes (5 hits) vs. 0 HP / 0 Def Magnemite: 5-15 (26.3 - 78.9%) -- approx. 12.1% chance to 2HKO
(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3)
196 Atk Minccino Tail Slap (5 hits) vs. 0 HP / 0 Def Magnemite: 10-15 (52.6 - 78.9%) -- guaranteed 2HKO
(2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3)
196 Atk Life Orb Minccino Tail Slap (5 hits) vs. 0 HP / 0 Def Magnemite: 15-20 (78.9 - 105.2%) -- approx. 6.3% chance to OHKO
(3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4)
Practically speaking I would say that aipom is better overall, but I don't agree that it completely outclasses minccino. The small amount of bulk aipom has over minccino can be important. Although aipom can not reliably damage 16 def. walls if it's jolly it would also lose out on the chance to speed tie with abra and ponyta by running adamant. The times that minccino has a opportunity to out damage aipom aren't very common but they do exist. Overall I feel that minccino is worthy of moving into C rank.
Oh, here is a quick example to show aipoms superior bulk when they are stranded without eviolite and force to let fletch hit them. This is already getting too long so I won't show more than this.
196+ Atk Fletchling Acrobatics (110 BP) vs. 76 HP / 0 Def Minccino: 18-22 (78.2 - 95.6%) -- guaranteed 2HKO
(18, 18, 19, 19, 19, 19, 19, 19, 19, 21, 21, 21, 21, 21, 21, 22)
196+ Atk Fletchling Acrobatics (110 BP) vs. 76 HP / 0 Def Aipom: 16-19 (69.5 - 82.6%) -- guaranteed 2HKO
(16, 16, 16, 16, 16, 16, 16, 16, 18, 18, 18, 18, 18, 18, 18, 19)
Here's pawniards ridiculous LO sucker punch.
236 Atk Life Orb Pawniard Sucker Punch vs. 76 HP / 0 Def Minccino: 21-25 (91.3 - 108.6%) -- 50% chance to OHKO
(21, 21, 21, 21, 21, 21, 21, 21, 23, 23, 23, 23, 23, 23, 23, 25)
236 Atk Life Orb Pawniard Sucker Punch vs. 76 HP / 0 Def Aipom: 17-21 (73.9 - 91.3%) -- guaranteed 2HKO
(17, 17, 17, 17, 17, 17, 19, 19, 19, 19, 19, 19, 19, 19, 19, 21)
Edit: Updated in response to some of KM's remarks.