From Worms Knowledge Base
Despite its threatening name, this weapon looks like a tiny, innocent mushroom. Well, not that innocent.
When used, it drops like a dynamite, and stops moving as soon as it encounters terrain. If it hits anything else than terrain, it harmlessly pops and disappears.
The Atomic Mushroom grows by a random amount every cycle of turns, and behaves much like an oil drum, it explodes when damaged, dealing an amount of damage proportional to its size. A small mushroom would inflict around 10 damage, and a large mushroom would be able to deal up to 30 damage. When its size reaches a certain limit, it will also automatically explode.
When a mushroom explodes, it releases spores. The bigger the mushroom is, the more spores it releases when it blows up. A tiny mushroom does not release any spore, and a fully grown mushroom may release up to 6 spores at once. Spores float around, following the wind (quite similarly to fire), and latch to terrain, disappearing into the ground. They can be easily destroyed by blowing up the bit of terrain they latched to. If there are too many spores close to each other, only one survives and the others die.
If a spore manages to survive, it grows into another Atomic Mushroom after one cycle of turns, and so on.
Although this weapon might seem underpowered, it can be used to distract the enemy, forcing them to clean up the potential threat before it multiplies itself. A single mushroom might end up infesting an entire portion of the landscape, leading to deadly explosive chain reactions. Since spores are invisible, eliminating an advanced mushroom infestation can be extremely hard, and a possible yet risky move in Forts mode would be to plant a mushroom on your own fort and blow it up when the wind is favorable, sending spores to the enemy fort.
The only possible issue with that weapon is resource usage. Hopefully, density control should properly regulate the total amount of spores and mushrooms on the landscape, as spores which are too close to each other are eliminated.