The Mycelarium rain bonus is that rain falls at night and, while it rains, hyphae shots cost no water at all. Growth is also at its fastest then. That combination makes the rainy night the best time to expand — and the cheapest time to farm unlock points.
Mycelarium rain bonus: what the rain changes
- Shots are free. The game's own on-screen tip says it: "Hyphae shots don't cost any water during the rain."
- Growth is fastest. This is why players queue up new roots at night in the rain rather than during the day.
- You can keep firing. Because the water price drops to zero, the usual reason to stop shooting — running the pool dry — disappears for the night.
Farming points in the rain
Points are paid for growing hyphae, and they keep coming from the same node if you keep growing from it. That means the Root Mushroom, which fires hyphae out of one spot, can be spammed at the same spot during a rainy night for free, farming unlock points indefinitely. Players flagged it as feeling broken, but it is the fastest way to fill the POINTS counter.
If you are not sure where those points come from in the first place, the unlock points guide covers the whole mechanic.
What to spend the points on
Points buy nodes in the upgrade tree, and the tree is the only thing in the game that turns time into progress. The one thing to decide first is which node to take, because the branch structure decides what each of them opens up. That is in the upgrade tree guide.