Doom Seed

The Doom Seed is a biological weapon created by Doctor Robotnik while he was based on Flickies' Island. From a single seed, it could sprout millions of gigantic vines to engulf entire cities. Furthermore, it had the ability to sense attackers, allowing it to counter-attack.

History
Robotnik had Agent X plant the Doom Seed beneath the streets of Metropolis City, where it soon sprouted and overran the city above with enormous vines. Sonic, Amy and Tekno managed to find the Doom Seed before it completely engulfed the city and Amy destroyed it by firing a crossbow bolt with weedkiller tied to it. With the seed dead, the weeds died as well. Metropolis resident Gilbert Grumpy used the dead weeds in his garden as compost.