To get a variant piñata, you have to feed it something.
Here are the list of 5 species that would be some of fastest residents:
Total 15 Variants possible of these i listed, so you should be able to get 5 of these.
Whirlm:
Purple: Turnip
Green: Watercress seed
Red: Water Lily seed
Taffly:
Yellow: Buttercup seed
Purple: Blackberry seed
Green: Poison Ivy flowerhead
Sparrowmint:
Pink: Water Lily flower
Green: Watercress flower
Purple: Thistle flowerhead
Candary: (Evolved from Sparrowmint feeding it a buttercup)
Pink: Water Lily seed
Blue: Bluebell
Green: Gooseberry
Bunnycomb:
Yellow: Pumpkin
Green: Gooseberry seed
Pink: Water Lily flower