Local Battles
Set Bots To Max and Extreme
Place a weight on the Up Arrow on your keyboard to make your car drive forward and afk. i used my phone leaning on a remote
you get xp every time you die and for distance driven
plus a bunch of other things that will give you small boosts
you want to do this until you hit level 10
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Classic mode is unlocked at level 2
this gets you a little bit more xp
Chaos mode is unlocked at level 5
this gets you endless xp when the bots get stuck
Custom mode is unlocked at level 10
this is the best game mode for xp farming, because its easy to get the bots stuck
once you unlock Custom mode use these settings

try to put sharp turns and use all the traps right after checkpoints. fans and bouncy traps work best. what we are trying to do is get the bots to all die right after the checkpoint for an endless experience loop

for the drive every car achievement you only need to load the level, can quit right away and move onto the next car