Both Alisa and Toy Freddy have different curses....and these curses are horrible without the other to counteract them.

Alisa,due to her curse,tends to feel sad. Really sad. She turns wherever she goes into a frozen wasteland if she gets sad enough,and eventually turns into an ice monster. Her sadness can affect thr tides,causing them to get huge and frigid cold,and making the whole Sea of  Thieves dangerous to sail.

Toy Freddy,on the other hand,his curse fills him either unbelievable amounts of rage. He often destroys things by accident during his outbursts,causing him to get more angry,it's a vicious cycle. Due to going to The Devil's Roar that fateful day,his anger can spark massive volcanic eruptions and even turn him into a monster made of Magma and lava.