For Mishimono

Bisharp @ Focus Sash
Ability: Defiant
EVs: 4 HP / 252 Atk / 252 Spe
Adamant Nature
- Knock Off
- Sucker Punch
- Iron Head
- Protect

Keldeo-Resolute @ Life Orb
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Scald
- Secret Sword
- Quick Guard
- Protect

Thundurus @ Sitrus Berry
Ability: Prankster
EVs: 244 HP / 108 Def / 64 SpA / 72 SpD / 20 Spe
Calm Nature
- Thunder Wave
- Thunderbolt
- Hidden Power [Ice]
- Taunt

Aegislash @ Safety Goggles
Ability: Stance Change
EVs: 252 HP / 4 Def / 252 SpA
Quiet Nature
IVs: 0 Spe
- Shadow Ball
- Flash Cannon
- King's Shield
- Wide Guard

Entei @ Choice Band
Ability: Pressure
EVs: 252 Atk / 4 SpD / 252 Spe
Adamant Nature
- Sacred Fire
- Stone Edge
- Extreme Speed
- Bulldoze

Latias-Mega @ Latiasite
Ability: Levitate
EVs: 248 HP / 252 Def / 8 SpA
Bold Nature
- Calm Mind
- Substitute
- Stored Power
- Roost

Made by Roxer-senpain :]

The core Keld + Sharp is great vs a bunch of things (as you stated in your post), so I made a team that made use of the core's ability to deal with a wide variety of threats, there's a bunch but you seem to be well versed in Pokemon so you can guess them yourself. You mentioned the core is weak vs bulky waters and Thundurus, while Entei may be weak against bulky waters, every other member of the team does well against them.

To play this team you just need to try to make Mega Latias setting up a viable win condition with the tools presented, Entei helps a lot since he can just nuke shit controled by Thundurus, Bulldoze is niche vs Heatran, you can remove it if you like for Flare Blitz but Tran was too big of a threat, this is because most Trans come in the field paired by something that can beat keldeo so he wont be as good of a check 100% of the time.

In short, create win conditions using Keldeo, Bisharp and Entei so Mega Latias can setup. Use Thundurus and Aegis to aid their teammates with whatever they need to do, also use them as bulky pivots to control the momentum of the match and/or create plays.
(You can also just spam entei sacred fire and watch shit die, and when lando-t comes in just kill it with something else)