Algodoo

An Evolution Simulator where marbles learn to fight against The Twins from Terraria!

Whenever the marbles deal a certain amount of damage, their hit accuracy is checked, the percentage of the shots they hit recently is equal to the chance that they will reproduce. The damage threshold required to check shrinks with smaller populations, and grows with bigger ones.

Their aim evolves as well. They can predict where The Twin will be by the time their arrow lands, or shoot more upwards to compensate for gravity.

The Twins are much deadlier than in real Terraria to make up for the marble's agility.