With the exception of the Cars and Finding Dory Worlds, each world has buddies that you unlock by getting enough points in each level, they're useful to get more points and Buddy Coins to unlock Playable Characters, here's a guide for finding them all in each level
Warning: This game is pretty glitchy in terms of the achievements, most of the time, you'll only get 1 achievement after you beat a stage, even though a lot of times, you'll should have gotten multiple at once. So i don't recommend going for a lot of achievements until you get a good chunk of the easy ones
If you're having trouble with the achievements popping, beat the Daycare Dash level as Buzz and it will force the achievements to pop (for whatever reason), you'll need to unlock Buzz in Daycare Dash first, so don't worry about collecting achievements for now, just enjoy the game for a while and then go for the achievements.