It's very cool to see how the drawing even without great rendering, if the terminator and perspective are correct, they'll end up looking pretty nice.

I did the assignment quick enough, but delayed in posting them.

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Let's do this!

Great start! I love testing new stuff too. Since you're working digitally, try flipping the image every once in a while, so you can see spot some mistakes more easily. In this one I can see that the right side of his body could use some perspective, it feels like he is face the viewer but his shoulders indicate his body is facing slightly to the right. And the right wing too could use some twisting 😉

The drawing looks great! Only thing that's bothering me are the human nails on his hands 😅

Well without comparing the two that looks fantastic but since you're drawing Lennon based on that picture what I can point out are the tones on his face are a little darker on yours and the proportions and placement of the features are a little bit off.