The Jello type is super-effective against and resists the Poison and Ground types, owing to how easy it is for gelatinous substances to absorb particles or liquids such as dirt and sludge respectively.
The Jello type is also super effective against the Fire type, since a large amount of jelly could easily smother a fire.
The Jello type is weak to and resisted by the Steel and Bug types, inspired by metal tools being used to slice gelatin, and bugs being able to burrow through gelatinous substances, such as ants being able to burrow through the gel in ant farms.
The Ice type is super effective against the Jello type as well, because cold temperatures often freeze gelatin solid.
The Jello type is resisted by the Water type, inspired by how water is a crucial ingredient in most gelatin recipes.
The Jello type is also resisted by itself, since attacking gelatin with gelatin just increases the total amount of gelatin.
The Fighting and Rock types are not very effective against the Jello type, due to the fact that if you punch or throw a rock at a block of gelatin, both will probably just bounce off of it.
