Ninjask is outclassed by Scolipede because the latter has better offensive presence. Its Stealth Rock weakness also isn't as crippling:
-Megahorn
-Spikes/Toxic Spikes
-Swords Dance/Toxic Spikes
-Baton Pass/Earthquake/Rock Slide
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Focus Sash
Ability: Speed Boost
or
-Swords Dance/Iron Defense
-Protect/Megahorn
-Substitute/Megahorn
-Baton Pass
Nature: Timid/Jolly
EVs: 248 HP/208 SDef/52 Spe
Item: Mental Herb/Black Sludge
Ability: Speed Boost
Blissey is terrible for an offensive role because its Special Attack isn't high enough to make the most of its wide movepool. It's better left to support roles on the team:
-Aromatherapy/Heal Bell
-Soft-Boiled
-Seismic Toss/Flamethrower
-Toxic/Thunder Wave
Nature: Bold
EVs: 4 HP/252 Def/252 SDef
Item: Leftovers
Ability: Natural Cure
As I told you in your profile, Smack Down is a terrible option for Conkeldurr. It's weak and Flying Pokemon hate Ice Punch and Stone Edge even more; the latter is even twice as strong as Smack Down. Assault Vest or Bulk Up are the best ways to use it:
-Drain Punch
-Mach Punch
-Knock Off
-Ice Punch/Stone Edge
Nature: Adamant
EVs: 188 HP/252 Atk/48 SDef/20 Spe
Item: Assault Vest
Ability: Guts
or
-Bulk Up
-Drain Punch
-Mach Punch
-Knock Off/Stone Edge/Ice Punch
Nature: Adamant
EVs: 252 Atk/4 Def/252 SDef
Item: Leftovers
Ability: Guts
Take note that Mega Tyranitar has enough Speed to use Dragon Dance effectively, so you might as well do that:
-Dragon Dance
-Stone Edge/Crunch
-Ice Punch/Crunch
-Earthquake
Nature: Jolly
EVs: 252 Atk/4 Def/252 Spe
Item: Tyranitarite
Ability: Sand Stream
Without Dragon Dance, Mega Tyranitar is slow. If you don't want to use Dragon Dance on it, you might as well make do with regular Tyranitar:
-Stone Edge
-Crunch
-Pursuit
-Earthquake/Ice Punch
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe (Jolly) or 180 HP/252 Atk/76 Spe (Adamant)
Item: Choice Scarf (Jolly)/Choice Band (Adamant)
Ability: Sand Stream
or
-Crunch
-Stone Edge/Ice Beam
-Earthquake
-Stealth Rock/Fire Blast
Nature: Impish/Relaxed
EVs: 248 HP/252 Def/8 SDef
Item: Leftovers
Ability: Sand Stream
For Assault Vest Azumarill, Power-Up Punch is the superior option over Brick Break, as AV Azumarill isn't as strong as the Choice Band and Belly Drum variants. Play Rough already handles Dragon Pokemon, while Waterfall and Aqua Jet already cover Gliscor and Landorus, so there's no reason to use Ice Punch. Azumarill also likes its priority Aqua Jet:
-Aqua Jet
-Play Rough
-Power-Up Punch
-Waterfall/Knock Off
Nature: Adamant
EVs: 16 HP/252 Atk/240 SDef
Item: Assault Vest
Ability: Huge Power
Here's Choice Band and BellyJet Azumarill if you're interested:
-Waterfall
-Aqua Jet
-Play Rough
-Superpower/Knock Off
Nature: Adamant
EVs: 164 HP/252 Atk/92 Spe
Item: Choice Band
Ability: Huge Power
or
-Belly Drum
-Aqua Jet
-Play Rough
-Waterfall/Superpower
Nature: Jolly
EVs: 4 HP/252 Atk/252 Spe
Item: Sitrus Berry
Ability: Huge Power
And as for your replacements:
Eruption Heatran can only have a Quiet nature, as the Pokemon Ranger event set it that way. Outside of Trick Room teams, Eruption Heatran is worthless:
-Lava Plume
-Protect
-Taunt/Roar/Stealth Rock
-Toxic/Will-o-Wisp
Nature: Calm
EVs: 248 HP/8 Def/252 SDef
Item: Leftovers
Ability: Flash Fire
or
-Fire Blast/Overheat
-Flash Cannon
-Earth Power/Stone Edge (latter Choice Scarf only)
-Flamethrower/Fire Blast/Hidden Power (Ice)
Nature: Modest
EVs: 252 SAtk/4 SDef/252 Spe
Item: Choice Specs/Choice Scarf
Ability: Flash Fire
While Mega Aggron is bulky enough for Metal Burst and Counter, it's not worth it because both moves rely on Aggron being attacked. Once your opponent sees what this Aggron is up to, they'll use it as setup bait:
-Stealth Rock
-Heavy Slam/Iron Head
-Thunder Wave/Ice Punch
-Earthquake/Rock Slide
Nature: Relaxed
EVs: 252 HP/16 Def/240 SDef
Item: Aggronite
Ability: Sturdy
or
-Rest
-Sleep Talk
-Heavy Slam/Iron Head
-Earthquake/Ice Punch
Nature: Relaxed
EVs: 252 HP/16 Def/240 SDef
Item: Aggronite
Ability: Sturdy
Though Scizor's Aerial Ace benefits from the Technician boost, it doesn't see much use besides hitting the occasional Breloom and Chesnaught super effectively. Flying spam is better left to Talonflame and Mega Pinsir (and to a lesser extent, Staraptor):
-Swords Dance
-Bullet Punch
-U-turn/Bug Bite/X-Scissor/Knock Off
-Roost
Nature: Adamant
EVs: 248 HP/136 Def/104 SDef/20 Spe
Item: Scizorite
Ability: Technician
or
-Swords Dance
-Bullet Punch
-U-turn/Bug Bite
-Knock Off/Superpower
Nature: Adamant
EVs: 252 Atk/4 SDef/252 Spe
Item: Scizorite
Ability: Technician
or
-U-turn
-Bullet Punch
-Superpower
-Pursuit/Knock Off
Nature: Adamant
EVs: 248 HP/252 Atk/8 SDef
Item: Choice Band
Ability: Technican
or
-U-turn
-Bullet Punch/Knock Off
-Defog
-Roost
Nature: Impish
EVs: 248 HP/252 Def/8 SDef
Item: Scizorite
Ability: Technician
Metagross has fallen out of favor because it never changed throughout the generations, while the metagame around it has. Not only that, but its best move, Meteor Mash, got nerfed and Metagross is now weak to Ghost and Dark. So I wouldn't really bother with it. But if you insist on using it, here's the best it can do:
-Meteor Mash
-Zen Headbutt
-Earthquake
-Pursuit
Nature: Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Assault Vest
Ability: Clear Body
or
-Stealth Rock
-Meteor Mash
-Earthquake
-Zen Headbutt/Pursuit/Trick
Nature: Adamant
EVs: 252 HP/252 Atk/4 SDef
Item: Leftovers/Iron Ball
Ability: Clear Body
I will heed your advice on Ninjask, Azumarill, and I will use D Dance Tyranitar. It's my first time using Azumarill so I don't know much about it, however I will continue to say I prefer Smack Down on Conkeldurr solely for the reason of pokemon with levitate that would otherwise take 3-4 turns to KO over 2 turns depending on the flow of battle up to that point. I'll switch out Scizor's Pursuit for Roost since Pursuit was just a placeholder in my mind for the sake of having 4 moves. Blissey is one of my best in battle because even with it's mediocre SpA it still 2 hits most pokemon, covers a lot of types, and with Serene Grace there's a greater chance of the moves' statuses being inflicted which can change the tide of battle greatly, however I do need to switch Grass Knot with Psychic.