100% achievements guide for Doodle Derby, includes some tips on how to get certain achievements easy way
Simply finish any Singleplayer race (multiplayer may work as well)
Go to multiplayer and host a game.
This could be in singleplay or multiplayer, just collect any key.
Have over 3 keys available at the same time. Probably easiest way is to host your own multiplayer game, since you can easily edit the level layout there with parts.
Find and collect a map (again, probably easiest to do in your hosted game, i used level Colosseum). They are scattered across multiplayer and singleplayer levels, sometimes hidden behind blocks (which requires destroying them).
The beast is literally the name of the Multiplayer level. Collect couple of maps to unlock it. Again, some maps are hidden behind blocks.
Complete any singleplayer level under specific time, for example: complete level 1 under 0:07.70 seconds.
Complete level 10 of singleplayer campaign (it requires 3 golden medals to unlock it).
You will get this while playing singleplayer mode eventually. Simply place 50 parts on any level (can be restarted multiple times).
You have to respawn 100 times. Singleplayer seems best as you can die and respawn pretty fast.
Same as THE DETERMINATOR but this time its 500 deaths.
Unlock all of the cars with keys. You will need 14 keys to do so.
Unlock all of the cars and parts by using keys. Majority of the keys can be easily obtained in Multiplayer. However, to finish this you will need to grab few from Singleplayer as well.
Some keys are hidden inside other blocks. There is few more keys than needed for this achievement.
Go to Singleplayer and level editor. Then create and save your own level (save, not upload).
Same as with ROADWORK but this time upload the level.
While on the topic of level editor, to get this achievement simply change background multiple times in a row (around 20 times or so).
Normally you would need to play and with 10 online races, however, since almost no-one plays this game you can go ahead and skip that.
Instead go into Multiplayer, host your own game and connect gamepad or other controller and play with yourself. It’s even faster if you do Party Game and use your own levels.
Create custom multiplayer game settings (Options/Gameplay/General). Thanks to developer for explaining this one.
You need to complete the level as Love Carriage. On multiplayer levels a heart may show up after using the magic wand power-up on certain blocks. It may be necessary to complete some level first (maybe even collect the piggy) and try it on next level. Just be sure not to lose the Carriage.
Obtain around 2000 points by doing tricks in multiplayer and finish the race.