Why are you using random EV spreads? Do they accomplish anything specific? (achieving OHKOs/2HKOs or avoiding being OHKOed/2HKOed by certain attacks, I mean) If not, I'll have to suggest better EV spreads for you.
You're better off using Roost on Togekiss over Nasty Plot. It seems tempting to make Togekiss hit harder, but you're better off restoring your health from time to time because without Roost, Togekiss gets worn down fast, and any defensive Pokemon that has access to reliable recovery has to use it for that reason. The EV spread for Togekiss should be 248 HP/252 Def/8 SDef with a Bold nature, but Calm with 248 HP/8 Def/252 SDef works too.
Even though Weakness Policy seems tempting to boost Dragonite's offenses to dangerously high levels, it's not worth it because even though Dragonite has access to Roost, passive recovery from Leftovers helps in the long run better than the +2 boost in both offenses. If Dragonite is forced out, the boosts will be lost. So Weakness Policy gets a no from me. Also, here's a better take on bulky Roost Dragonite:
-Dragon Claw
-Fire Punch/Superpower/Earthquake
-Extreme Speed
-Roost
Nature: Adamant
EVs: 216 HP/64 Atk/228 SDef (this spread gives Dragonite the most optimal special bulk possible, while still giving it power; bulky Roost Dragonite doesn't need Speed)
Item: Leftovers
Ability: Multiscale
Medicham sits at a good Speed tier of 100. Why are you wasting that away by investing in bulk? Its bulk isn't that good, so bulk investment is pointless. 252 Atk/4 Def/252 Spe is the way to go in this case.
Scolipede is doing too much at once, really. It's massive Taunt bait, and you don't have Mental Herb to save it from that. Again, what purpose do the EV serve? Toxic Spikes should only be used on balanced/defensive teams and it clashes with Togekiss' Thunder Wave. Here's a better take on BP Scolipede:
-Substitute
-Protect
-Baton Pass
-Swords Dance/Iron Defense
Nature: Timid
EVs: 248 HP/20 Def/240 Spe
Item: Mental Herb
Ability: Speed Boost
While Chansey can lure in physical attackers to use Counter on, there are times when those attackers don't attack at all and set up on Chansey, making Counter a wasted move in that instance. Seismic Toss is always the preferred consistency attack, and the preferred EV spread is 4 HP/252 Def/252 SDef for better all-round bulk.
Curse Ferrothorn needs tons of support to work effectively; it needs Fire or Fighting Pokemon removed for it to do its thing, but you don't have much of that. You're better off having it lay down entry hazards in the form of Stealth Rock and forgoing Curse entirely:
-Stealth Rock
-Leech Seed
-Power Whip
-Gyro Ball/Protect/Knock Off
Nature: Relaxed
EVs: 252 HP/88 Def/168 SDef
Item: Leftovers
Ability: Iron Barbs
Since Dragonite is weak to Stealth Rock, try to squeeze in a Rapid Spinner/Defogger on the team; the aforementioned moves remove entry hazards. Or you can just squeeze in Defog on Togekiss, preferably over Dazzling Gleam, as it's rather expendable. If you have your doubts on Excadrill, remember that it and Dragonite resist each other's weaknesses:
Tentacruel:
-Scald
-Acid Spray
-Sludge Bomb/Knock Off
-Rapid Spin
Nature: Bold
EVs: 252 HP/224 Def/32 Spe
Item: Black Sludge
Ability: Liquid Ooze
Starmie:
-Hydro Pump
-Psyshock/Thunderbolt
-Ice Beam
-Rapid Spin
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb/Leftovers
Ability: Natural Cure
or
-Scald
-Reflect Type
-Rapid Spin
-Recover
Nature: Timid
EVs: 248 HP/20 Def/16 SDef/224 Spe
Item: Leftovers
Ability: Natural Cure
Mandibuzz:
-Foul Play
-Roost
-Whirlwind/Taunt
-Defog
Nature: Bold
EVs: 248 HP/136 Def/108 SDef/16 Spe
Item: Leftovers
Ability: Overcoat
Excadrill:
-Earthquake
-Iron Head
-Rock Slide
-Rapid Spin
Nature: Jolly/Adamant
EVs: 252 Atk/4 Def/252 Spe (Jolly) or 120 HP/136 Atk/252 SDef (Adamant)
Item: Choice Scarf (Jolly)/Assault Vest (Adamant)
Ability: Mold Breaker
Latios:
-Draco Meteor
-Psyshock
-Surf/Thunderbolt/Hidden Power (Fighting)
-Defog
Nature: Timid
EVs: 252 SAtk/4 SDef/252 Spe
Item: Life Orb
