What is the biology behind a skin "mole"?
A mole is simply a benign tumour, i.e. a proliferated cell growth that hasn’t become cancerous. So moles are not dead cells, they are very much alive. The colour is caused by a high concentration of the melanin, which is also responsible for normal darker skin.

Since moles are tumours, they can – but in most cases don’t – give rise to melanomas, malignant skin tumours, when they lose susceptibility to cell growth regulation and start invading surrounding tissue.

Scar tissue is entirely unrelated and due to regular regrowth of epithelial cells after injury forming a linear collagen structure (as opposed to the skin’s normal collagen structure, which resembles a “weaved“ structure).