Two days back we had one... and the topics were
1) A crocodile sneaking up on a rubber duck with a red band around its neck. (half an hour, color, limited background)
2) A kid wearing his underwear sucking his toe.(fifteen minutes, only line art)
and here's my attemt at the two... i couldn' finish the first one... i spent too much time making the bubbles and trying to make the marble texture... i'll finish that one sometime soon and post again...
Line art is my favorite round because i can finish the sketch in time, and i can add detail... :D
the third one is my preliminary sketch of the concept... over which i applied some watercolor later on... i wished i could achieve the same in photoshop... :P