The plural form of oddity is oddities.

What is a irregularity?

1 : something that is irregular (such as improper or dishonest conduct) alleged irregularities in the city government. 2 : the quality or state of being irregular. 3 : constipation.

What is Addity?

an odd or remarkably unusual person, thing, or event. the quality of being odd; singularity, strangeness, or eccentricity. an odd characteristic or trait; peculiarity.