I feel like this could easily be expanded upon with a few more missions and maybe some alternate weapons or parts for you mech. Just simple stuff like parts that prioritize 1 mode over the other, like more plane or mech maneuverability. The core mechanics and idea are very fun though.
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also for some reason the game started crashing, specifically when I died or started/ended a level. Also a quick suggestion is to give the mech some weapons that help one form over the other. Like droppable bombs that do lots of damage to ground targets but are really only good as a plane, and melee weapons for the mech form