I participated in a Game Jam. There were 9 people and we had 2 days to create a 2D tower defense game. This game is played on Windows PC and Android.
You can create one tower at the beginning on every level. When you kill the enemy, you will get gold to buy other towers and gems (these are the boosts).
The enemys and the towers have one color from 4 (red <=> blue, green <=> yellow). The enemys' color is fixed, but you can change the towers' color. The tower, which has the opposite color, has a higher damage.