The user has the power to induce disastrous events onto any kind of event. They could make celebrations where everyone is having fun turn into a riot or a constructing of a house going according to plan turn into a disaster that results in the house being destroyed. Anything good can be made into a bad situation. As Murphy's Law says, what can go wrong, will go wrong.
Nemo (American Dad!) aka the "Antichrist" can cause calamities to happen from doing child antics.
Tooru's Stand, Wonder of U/Satoru Akefu (JoJo's Bizarre Adventure Part 8: JoJolion) generates the worst outcome possible, abnormal or not, when creating disaster/calamity to anyone who pursues him or works against him…
…The activation of the ability is so sensitive, as even the feeling or idea of doing anything remotely wrong to him, or even looking at the Stand's back, without any intent to harm, can still trigger the ability.
Jack the Drought (One Piece) earned his nickname for whenever he rampages on an island, it is left in a decaying state akin to a drought.
Queen the Plague (One Piece) created the contagious biological weapon, Mummy, that spreads rapidly, hence a plague.
King the Conflagration (One Piece) is one of the three Disasters, like Jack and Queen.
Sheriff Murphy (Milo Murphy Law) is both the original murphy and the origin of Murphy's Law…
…That pass down to Milo Murphy and all the other male people in his Family have Murphy's Law.
Hou Ken (Kingdom)
Calamity (Valkyrie Crusade) the embodiment of calamity.
Dice's (Valkyrie Crusade) powers are linked to her mood, bringing either great luck or great calamity depending on how she feels.