This tutorial shows how to make deformer spline by using "Spline Mask"
[Mograph]Spline Mask
Step 1: Add the metaball objet from objects >modeling > metaball or select the metaball object from the standard objects icons.
Step 2: Select the Metaball object, then change the object's attributes. Set Hull to 289%
Step 3: Add a Spline Mask from the Mograph objects as a parent of the circle spline (set radius to 113), and a child of the metaball object. The spline mask is a boolean operator, and as such needs a "B" value.
Create a spline object > Flower (set radius to 300) and add it to the spline mask as a child in the "B" or second position
Step 4: Change the Spline Mask object property:
Mode = A Union B, axis XY (along Z)
Step 5: Now, time to start the animation! Press the Automatic Keyframing button.
Step 7: Now, select a spline object (Flower) In the Attributes Manager fill in inner radius to 500
then Press the Automatic Keyframing button to stop the animation
Final result
Step 6: Drag the Animation Bar to the right until it ends on 50 F.