2D Shooter Part 2

Modifications:

- new Desert theme

- added background image to the main menu reflecting the new theme

- added Instruction page

- addition of third level which would be more challenging

- adjusted enemy health and spawner variables to balance difficulty

- re-skinned enemies, player and their animation using free asset from itch.io:

https://alakon.itch.io/pixel-pack-desertcowboy

https://ansimuz.itch.io/spaceship-shooter-environment

- re-mapped each polygon collider to reflect new skin

- addition of extra level with endless mode where player can keep playing until death

 Credits:

Created by David Oh (Hyunsuk Oh)