Will increase a villager's XP by 100. To use: Tap on a villager and click the Use item button in the pop-up info.
When you give your villager mushroom grog, they will gain 100 xp. If they had less than 100 xp to go before reaching the next level, they will level up and have a birthday. Keep in mind though, that if you give them mushroom grog when they have less than 100 xp to go before reaching the next TWO levels or more, you'll only get to celebrate one birthday even though they leveled up several times.