Currently, you always want to train 4 of the same model at once, so you can use it in up to 4 simulators. But if you want to expand, you have to kill lots of mobs again.

Suggestion: Make it viable to train multiple different models at once by adding a "model trainer" block. This takes a "target" model of a higher tier and another model and takes energy + items (e.g., rotten flesh for a zombie model) and upgrades the second model, capped at the level of the "target".

This could extend the "neural networks" metaphor by being called adverserial training