I chose the Stoneflower because I have this cool new artwork (search for Custom Art by Smitty on Facebook). It also happens to feature prominently in the module I just released on RPGNow. When I was finishing up Denizens of the Citadel, I needed a monster that could be trapped for hundreds of years, but still be alive. It also needed to be a good encounter for low level (2-4th) parties. Digging through the Swords and Wizardry monster tomes, I came across the Stoneflower, and fell in love.
It doesn't do a lot of damage (d3). It can spread attacks around (1d6 attacks per round).It has a weird magnetic effect. A perfect monster, right when I needed it. Matt Finch does great work. Sometimes weird monsters are perfect monsters. . .