The Dizzy Dummy is the most popular obstacle for the third round. Basically, you spin until you're good and dizzy, and that first appeared in Season 1.
Then they complete an obstacle, and whoever wins that obstacle moves on. The remaining 5 get back on the Dizzy Dummy, spin, and run again but go on a different obstacle and do that, and when that's done, they do it again, until there are 4 people moving on.
In Season 2, they have the Dizzy Dummy 2.0, which is basically the same as the regular Dizzy Dummy, only they have to go through a keyhole, door, bungee web, or a football post to get throughout the course.
On (S1x3) contestant Jarren Joshu had thrown up on the Dizzy Dummy causing him to drop out of the running for $50,000. As he stated in his interview with Jill, "I gave everything I had and a little bit more." Causing to him to win a Wipey for "Dizziest Dummy" and this moment ranked in at #3 on Wipeout's Top 25 Moments.