The reason there isn't anything from Hardmode is because I imagine that if there where to be a Terraria movie, everything in Hardmode would be saved for the sequel.
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Evil Ghost Lady
Simple🌳
The Eye of Cthulhu would probably appear as a large eyeball too cartoon-ish that it's uncanny. The background is just black, the greenscreen lighting is terrible, and the player says "Oh no" with a near-nonchalant tone before the eyeball begins to float towards the player like it's a claw in an arcade toy machine.
Golden Heretic Snakeboat
God Damn it stop making me want a terraria movie
Ivyss
Skeletron head would just be some random skull jpg off Google images and the arms look like they were drawn by a three year old.