Multiplier tips?

[lufia22]

Do you guys have any tips for increasing the multiplier? It seems impossible to increase the multiplier with just the regular laser because you can't kill enemies fast enough. It feels random whether I can increase it or not based on which enemies spawn, when a power up enemy spawns, and which power up enemy spawns.

Some waves, like the light blue ships that turn into mushrooms on death, seem impossible to increase your multiplier on regardless of which power up you have.

I feel like I'm missing something.