I've noticed with a number of articles that the tense changes back and forth from present tense to past tense. Here's an example from Owlette's Feathered Friend. This is the first paragraph from the synopsis section, with words color coded blue for past tense and green for present tense.
Amaya, Connor, and Greg are in Greg's room playing with Lionel when suddenly, the HQ alarm sounded. They checked out HQ at night and discovered it was only a bird. When the bird flew off the branches in HQ she flew onto Owlette's arm. This gave Owlette the idea of making the bird a pet; and Owlette calls her Birdy.
The Editing Guidelines & Tips doesn't seem to declare a tense. I'm under the impression that synopsis sections and other content that summarizes an episode is typically done in past tense, because being a synopsis suggests that the actions have already happened: in which case episode pages would mostly be past tense, whereas character pages might primarily be present tense, depending on the situation.
I don't know. I was planning on editing some episode pages for tense consistency, and wanted to make sure I was choosing the right tense.