A 53.5 MPH Dickeephus taken for a strike by poor Wes Helms in 2010. (Thanks to Mike Fast for the image)
For most of 2010, R.A. Dickey befuddled opposing batters with 3* pitches: a fastball, a fast knuckleball, and a slow knuckleball. But on August 18th**, R.A. Dickey unleashed his third, most devastating knuckleball - the Dickeephus*** pitch -, striking out Geoff Blum swinging with a 62 MPH knuckleball. Dickey proceeded to throw 9 more Dickeephuses in 2010 (one on 8/24, two on 8/29, two on 9/14, one on 9/19, and 3 on 9/29) to mixed results. The Geoff Blum pitch was actually the fastest the Dickeephus would be for the rest of 2010 - these nine last Dickeephus pitches ranged from 53.3 MPH (a called strike against Wes Helms) to 58.1 MPH.
*Dickey actually has thrown a change-up each of the last few years, but it's really really rare and random. It's not worth talking about.
**Dickey actually threw two Dickeephus pitches before this date, on June 17 and July 15. But these were isolated incidents; his real use of the Dickeephus in earnest started on August 18th.
Figure 1 and 2: The Movement and Velocity of the Dickeephus in 2011. The Graphs are read from a catcher's point of view: so pitches with negative horizontal movement (on the left side of the graph) break INSIDE on right-handed batters while pitches with positive horizontal movement (on the right side of the graph) break AWAY from righties.
Note the wide range of movement on the Dickeephus here. This isn't a normal eephus pitch - this is something special.
Figure 3: The location of R.A. Dickey's Dickeephus pitches this year. The black rectangle in the center of the graph represents a large version of the strike zone. Like Figures 1 and 2, this graph is from a catcher's viewpoint.
Overall the pitch is in a wide strike zone roughly 50% of the time, which is pretty damn impressive.
The Dickeephus has been an awesome pitch: while batters swing at the pitch over half of the time (55.6%) - basically whenever the pitch has been in the strike zone, batters have swung. Despite the pitch being in the zone when batters swing, they whiff on the pitch a quarter of the time they swing, getting a swinging strike on 5 (13.9%) of these pitches, while batters have only put the ball in play 8 times this year. The end result has been a pitch that has been really effective this year. It probably shouldn't be thrown any more often than it has been (once or twice per game) - but as a surprise pitch, it is awesome.
*I'm defining the Dickeephus as any knuckler under 65 MPH.