Nicolai Czempin
"flash" the mass display or otherwise notify the player
disable (grey out?) the towers when not enough mass is available. when the player clicks on one anyway, some notification could be shown to point to the flashing(?) mass display
make a sound when someone tries to place a tower when mass is insufficient.
just collecting some feedback; some of these require general gameplay changes and may deserve (or already have) their own issues - The final wave is far too difficult. - Teach...
Backstory
While this game technically doesn't _need_ a story, it wouldn't hurt to have some kind of simple background story motivating the mayhem that happens in this game ;-) We could...
add a wave to the tutorial that explains blocking [and the effects of blocking an alien completely]
Right now the area outside the current map is simply drawn as black. There should be some cool effect to indicate that there really is some landscape outside our level,...