Mutant Seedling

 were NPC that gave event currency to get prizes. They were appearing on the streets of Player's Springfield and their Neighbors' Springfields. The player had different possibilities to collect from them. They were in the Terwilligers 2015 Event.
 * By tapping them on their own Town.
 * By dropping them in their Friend's Towns.

Rewards
Squished the Mutant Seed within 4 hours, the player AND his neighbor that left it would get one of the following: Mutant Seed disappeared if the player did not take care of them within the same 4 hours, so only his neighbor would get one of the following:
 * 8 Fertilizers or 8 Corns
 * 4 Spades, 4 Gas Masks or 4 Music Notes AND 8 Fertilizers or 8 Corns
 * 4 Fertilizers, 4 Corns, 2 Spades, 2 Gas Masks or 2 Music Notes
 * 2 Spades, 2 Gas Masks or 2 Music Notes AND 4 Fertilizers or 4 Corns

Trivia

 * A maximum of 10 mutant seeds could be found in your town at a time.
 * A maximum of 10 mutant seeds could be dropped in your friend's towns.
 * A maximum of 5 mutant seeds could be placed in your other Springfield (24 hours timer to payout).
 * Mutant seeds could be purchase from the store
 * 1 mutant seed for 1 Donut
 * 5 mutant seeds for 3 Donuts
 * 10 mutant seeds for 5 Donuts
 * 25 mutant seeds for 10 Donuts
 * Collecting 6000 Spades to reach the fifth stage during the Act One of the event rewarded the player with a pack of 50 mutant seeds.
 * Collecting 7800 Gas Masks to reach the sixth stage during the Act Two of the event rewarded the player with another pack of 50 mutant seeds.
 * Roaming mutant seedlings resemble Ursula Vernon's The Biting Pear of Salamanca aka "LOL WUT" pear.