A bat is one of the quickest Halloween drawings there is, because it is really just a silhouette. You draw the outline in four lines, fill it in black, and add two dots for eyes. The whole thing takes a couple of minutes, and once you can draw one you can draw a flock.
This walkthrough follows HalloweenDrawings on YouTube, shot straight down over white paper with a black marker. There is no shading and no colour, which is exactly why it works: a bat reads from its shape alone.
What you need
A black marker and paper. A fine tip for the outline and a chisel or broad tip for the fill saves a lot of scribbling. If you want fangs or wing lines afterwards, a white gel pen draws over dry black marker cleanly.
The shape in four lines
Two bumps for the ears. One long swept line out from each ear for the top of the wings. A row of U shapes back from each wingtip for the bottom edge, meeting under the head. That is the entire outline, and everything after it is filling in.
The scalloped bottom edge is the part that matters. It is the stretched membrane between the bat's fingers, and it is the single detail that separates a bat from a bird or a moth in silhouette.
Where it goes wrong
The head is too big. The wings should be five or six times the width of the head. Draw the ears small.
The wings do not match. Check both wingtips are the same distance from the head before you scallop the bottom edge. Extend the short side rather than erasing the long one.
The fill is streaky. Overlap every stroke and go over the outline rather than up to it. A dense, slightly messy black looks better than a careful one with gaps.
Making a flock
Draw the same bat at three or four sizes on black card, cut them out, and stick them up a wall or across a window in a curve. Because they are silhouettes, they read from across the room. A few with wings tilted at different angles look like they are flying.
More Halloween drawing
The same shape-first approach handles the rest of the season. A jack-o'-lantern is three triangles and a grin, and a scary ghost takes the opposite approach, building drama out of shading rather than silhouette. For the fundamentals underneath all of these, start with how to draw.