From Mario Fan Games Galaxy Wiki

Yoshimanyoshimanyoshimanyoshimanyoshiman is a forum event caused by Retriever II. Prior to the event, the sticky and regular topics were completely re-arranged in the first page of each forum. The event began when the CCC suddenly had every single topic title say "yoshimanyoshimanyoshimanyoshimanyoshiman." There-after, the event transformed into different stages, and at one point had "DJ Yoshiman" started every topic and making every last reply, and having "DJ Yoshiman" viewing every single topic. 20 minutes later, the CCC and all boards were reverted back to normal. How the event occurred is currently unknown.

Some believe the event to be similar to that of Earthbound's last boss, where RII was Giygas, and Yoshiman was Ness.

This event was an unrelated event to the final part of ZekeWeek, where Yoshiman as Giygas and Zekewars as Ness dueled in a special forum.