In order to understand that this is the same character that evolves, not two different characters, both must share a similar anatomy, adapted to their size.
Step 2
Sketch
Step 3
Give Vampbirtt the physical characteristics of the smaller Batbirtt but make them larger and more aggressive.
Step 4
Inking and Colour
Give Batbirtt a softer appearance by applying the ink in curves.
Step 5
Give Vambirtt a more angular look. The cool colours indicate that they are wicked creatures. The yellows and reds give the contract that the characters require.