Randall and Mike are facing each other, a classic battle between two mischievous monsters. Randall has a menacing jaw and fierce spiked back while Mike stands stubbormly with his wide open eye. You could add a level of intensity to Randall's look by coloring his purple skin a deep shade and his shirt a bright blue. Similarly, you could use a bright purple for Mike's shirt and a soft green for his skin. Outline Randall's spines with black and give Mike a hint of a grassy color to highlight his fiesty face. Add shadowing to deepen the colors and bring the two monsters to life with a creative flair. Bring out the indiviudal personalities of the two monsters by using complimentary and vibrant colors to tell their stories.