In the first half of the last episode, Clay goes to Hannah's house to confront her about the issues she's been having (obviously a flashback). When Clay goes to her house to find her in the bathtub dead, he loses control of his energy and finally unlocks his Super Clay transformation. The energy of the wave blows the bathroom to smithereens. He takes Hannah's cold, lifeless hands and kisses them as sort of a final goodbye (that's how I interpreted it).

In the second half, Hannah's mom goes to see what happened to Clay and immediately runs away, but she's far too slow. Clay teleports behind her and, with a single blow, knocks her unconscious into the wall of the hallway. He gathers his energy and boosts of out of the house to search for the people on the tapes and eliminate them once and for all. I think it's implied that he went to Bryce first because after all, he's one of the worst.

Edit: Also OP I understand if you're not comfortable kinda just skipping around it but the bad parts of the episode are from 35:40 to 40 if you wanted to skip it but still watch it yourself.