Harpy is good for that, just lunge at enemy or attacks and your belly get larger each time.
Viewing post in MonCurse V0.7 (+ Lamia) comments
Actually its based on the amount of eggs you have on you. (eggs being the special ability you get after you get harpy legs)the more eggs you have the bigger your belly is. i believe that 10 or so eggs was the maximum for the actual size, but got those results ages ago so i might not be correct on the 10 eggs being max.