main menu music: https://freesound.org/people/LittleRobotSoundFactory/sounds/274169/
intermission music: https://freesound.org/people/szegvari/sounds/560746/
mission music: https://freesound.org/people/FoolBoyMedia/sounds/270366/
victory sound: https://freesound.org/people/joshuaempyre/sounds/404024/

gun sound: https://freesound.org/people/CJDeets/sounds/476740/
cannon sound: https://freesound.org/people/Kneeling/sounds/448002/
power up sound: https://freesound.org/people/Breviceps/sounds/557593/
power down sound: https://freesound.org/people/qubodup/sounds/222372/
stomp sound: https://freesound.org/people/studiomandragore/sounds/401628/
crash sound: https://freesound.org/people/qubodup/sounds/182429/
impact sound: https://freesound.org/people/Oddworld/sounds/75328/
hydraulic sound: https://freesound.org/people/eardeer/sounds/385083/

mech sprite: https://opengameart.org/content/unit-666-mech
dead tree sprites: https://opengameart.org/content/knarled-trees
green tree sprites: https://opengameart.org/content/tree-collection-v26-bleeds-game-art
cannon effect: https://opengameart.org/content/blue-fire-effect
small explosion sprites: https://gaph.artstation.com/
large explosion sprite: https://www.freepngimg.com/png/31556-atomic-explosion-transparent-background
menu background and sky: https://free-images.com/lg/5434/planet_earth_moon_science.jpg
welder: https://opengameart.org/content/16-bit-alien
welding sparks: https://opengameart.org/content/spark-particles-set-of-8
skull and bones: https://openclipart.org/image/400px/1010
sky: https://svs.gsfc.nasa.gov/3895
moon: https://www.publicdomainpictures.net/en/view-image.php?image=44955&picture=full-moon-at-midnight-close-up
blue sky: https://www.pexels.com/photo/blue-and-white-sky-with-stars-4737484/

orbitron font: https://www.1001freefonts.com/orbitron.font
exoplanetaria font: https://www.fontspace.com/exoplanetaria-font-f41401