Sparrowmint

Once a Whirlm becomes a resident of your garden, that fulfills the conditions to attract the Sparrowmint to your world, but it won't enter the boundaries of your garden until you get a baby whirlm.

The condition for getting two Sparrowmints to do the romance dance is actually to feed each one a Whirlm.

Romance requirements: Has eaten one Whirlm. Have a Sparrowmint house in the garden.