Add new enemy types (and bosses)

[Kn1MS]

Is your feature request related to a problem? Please describe.
This is an idea of some sort. We need to make more enemy types to use them at level 3. We also need bosses for 2nd and 3rd levels.

Describe the solution you'd like
Find new sprites, make them right (I mean the source file should have a right order and size of its sprite animation pieces), make new enemies from them.

Describe alternatives you've considered
None.

Additional context
None.