Top 10 Best Boosters

1. Overgrown Foxy: Randomly boosts a certain stat every 4s, stacks and it has 3 placements!
2. Spring Duo: 
   Has 2 modes, a damage and range boosting one and a CD boosting one. One deals more DPS and the other focuses more on boosting. Great hybrid unit.
3. Old Man Consequences: Best water element booster, provides a 10% buff in CD and damage, and gives a 25% range boost. 
4. Golden Cupcake: 
   Gives 5% (caps at 15%) in all stats per light unit (stacks with itself.) Great unit to use if you are using light units like Valkyrie Chica and Mangle.
5. Puppet: 25% boost every 45s, not the best but comes in clutch if you use it during bosses.
6. Popcorn Bot: Junk boost but it stacks so it's decent.
7. Balloon Boy: 10% more range per placement (2) not good.
8. Movie Director Freddy: Boosts all unit's cash gain, and gives a 25% damage boost to one unit with the highest damage.
9. Cupcake: Boosts all stats by 3% (doesn't stack)
10. Party Packer Cupcake: Boosts damage and range by 3%.