Gloom Rats are one of the 'beasties' that occur during the game. They make a small area of your land have a red glow and the buildings inside will then take additional energy to collect/harvest.
Defeating the beastie removes the glow so a player may continually normally. Rats are commonly found when harvesting from your farms.
Rats are the easiest of the beasties, taking minimal hits to disband. They have 3 life, which takes 3 energy with normal hits, or 1 energy with the use of a Club.
They can be summoned with a Gloom Rat Potion.
They often drop Gloom Rat Tails which are required to create this potion.