Hmm... This might be a crazy idea that you are against, but if you could implement some sort of story mode with money and upgrades, this game might be more addictive to some.
my strategy for beating bosses (such as tyson in mission 4) includes using arrows and ranged units. when the boss comes close to the units, i use the arrows which pushes the boss back. rinse and repeat. it's important to note that this strategy relies on a high mana regen rate, not a high level arrow attack.
This game seems to be made in the style of mushroom madness (1 & 2) can anyone confirm that they are made by the same developer? Anyways, keep up the great work.
 "Mushroom Madness 3"){kind=icon}
 "Accelerator"){kind=icon}
 "Flight"){kind=icon}
 "endeavor"){kind=icon}
 "Frantic Frigates"){kind=icon}
 "Arkandian Revenant"){kind=icon}
 "My Little Army"){kind=icon}
 "Granny Strikes Back"){kind=icon}
 "Get Off My Lawn"){kind=icon}
 "RPG Shooter: Starwish"){kind=icon}
 "Insectonator: Zombie mode"){kind=icon}
 "Edmus"){kind=icon}
 "SeppuKuties"){kind=icon}
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I've actually been recently thinking about a story/adventure mode, with specific goals :)