Threes has random generation-as-you-go, so the game can be heavily save-scummed to manipulate the RNG. Saves can be found at AppData\LocalLow\Sirvo LLC\Threes. There's three main points of when to do so:

• Before a bag reset (it's pretty difficult to catch unless you were counting tiles). You'll notice save-scumming at different points and trying different moves might change the order of tiles.
  
• Right before getting triple tiles. The numbers will be different each time you try this, and you can just keep rolling for the highest possible (1/8th of current highest tile).
  
• During the triple tiles. It will be a random roll of the 3. And maybe some more RNG if you have choices in location.

The program linked in this guide can be used to help clean and optimize the board. Can't rely on it 100% though as it cannot account for the RNG of pieces.
https://www.trueachievements.com/a195751/volleo-achievement

The program linked in this guide can be used for the lock-achievements.
https://www.trueachievements.com/a195754/twelvelock-achievement#oSolutions

Game can be done in co-op. Alternatively, loading in someone's multiplayer session where the objectives were already met transfers completion progress to every player in the lobby. Taste of Adventure DLC is required.

https://steamcommunity.com/sharedfiles/filedetails/?id=1322272853

With money, timescaling, spawning guests, most objectives that don't require building something to meet a rating become trivial and instantaneous completions.

For Happiness, hire a bunch of entertainers.
For Experiences, people need to have all their needs met, until the point of leaving. This is far more difficult with bigger/more established parks.
For Decorations, there shouldn't be collision so you can just spam Large water towers around all the paths. Be sure to build walls around your depot center/bathrooms.

I did not test this in multiplayer.

https://steamcommunity.com/sharedfiles/filedetails/?id=3237773206
Having an Undo is pretty overpowered.

https://steamcommunity.com/sharedfiles/filedetails/?id=3174675348
Groups of vandals roaming the park do not spawn with this modifier.

Grinds like running ads, banning vandals, researching rides, can be done by saving before an instance and just reloading. Disaster Peaks gets a lot of vandals.

Wild Ride - can search Wild Ride in workshop (there's quite a few since they are ride specific), build one in sandbox, get a passenger on it, and idle until the achievement unlocks. The achievement specifically is for having a ride go on for a full in-game year.

Overly Attached - easily doable by deleting the path in front of the entrance and waiting 10 in-game years.

Fun out of 10! - Bobsled coaster recommended. Must be done without using a blueprint. Can reference workshop blueprints for what might work. Generally, build a long bobsled track without sharp turns and don't forget to angle some tracks so cars don't fly off.

https://www.trueachievements.com/walkthroughfull.aspx?walkthroughid=3310

https://steamcommunity.com/sharedfiles/filedetails/?id=2680779970

Complete Solution Guide

pi-2 solution

Levels are actually fixed generation (give or take a few levels like the last boss), so you could actually repeat inputs step-by-step to have the same outcome. "The very best" may require needing to do specifically a 4-chain by one trigger. I was not able to get it doing 3-chains.

Duels:
https://youtu.be/4svntX4Ayd0

Survivals:
https://youtu.be/-AkOD6oa7SM

Puzzles:
https://youtu.be/Bb_8Pd3-G3Q

Possibly troublesome achievements:
https://youtu.be/AxnpLGoPzSg
https://youtu.be/k004erJc40g
https://youtu.be/r8SCgl6lnrE

https://discord.gg/h9sGj6bdbY

Chat with us on Discord! We can be easily reached and worked with here. Hear about the latest bundles, shutdowns, delistings, free games, make friends and co-op partners all in this server~

RESTRICTED: Its single achievement is currently not implemented.

RESTRICTED: Multiplayer party game. Win on all maps and destroy the ship on 'Ice Breaker'. Can be done with an extra controller or an AI. 'La Bonnotte' is currently broken. ~25 minutes to 92%.

RESTRICTED: Soundboard software. Drag an audio file into the soundboard window, play it and upload to Steam Workshop. ~1 minute to 100%.

RESTRICTED: Awful shooter. Find 3 eggs and survive for 20 minutes on Medieval Ruins map. Tabbing out of the game pauses the game but leaves the timer running, making the survival trivial. ~20 minutes to 100%.