There are 10 levels that increase in difficulty.
In each level, you will fight enemies in waves until you win or die (in which case the level will restart). There is a timer you can use for measuring your level of success. After each level, you can pick one of three buffs that persist across levels: damage, speed, health.
Octopus. An underwater sea creature that does not like to be disturbed. Has 5 health and attacks by colliding.
Lightning Fish. A mutated fish charged by lightning. Has 5 health and attacks by shooting projectiles.
Crusteye. A other-worldly creature with one large eye. Has 3 health and attacks by colliding. Beware: This one is very fast.
Amphiptere. A poisonous snake feared by many. Has 5 health and attacks by colliding. Beware: This small enemy can easily evade your projectiles.
Fire (the literal embodiment). No one knows how Fire came to be; explorers tend to avoid this enemy at all costs. Has 7 health and attacks by colliding. Beware: This enemy can move very fast up and down and deals twice the damage of the others.
Moltus. Remnants of a destroyed planet that have reawoken. Has 5 health and attacks by colliding. Beware: This enemy can move very fast left and right.