This simple lightweight clip allows you to attach a mirror pane to the front of the Tello to give you a view looking straight(ish) down.
I'm trying to make the mirror as small as possible but may need to make it a little bigger as I can still see edges in these sample shots.
Because it's so small, I print at .15mm (and it prints very fast)
I cut an 18mm square from flexible plastic mirror sheets I purchased on Amazon, here's the link. It's very easy to cut with a fresh razor.
Note: I don't think the Tello is well suited to recording video via a mirror. The image stabilization they use seem to only work with the horizontal capture of video as the reflected image suffers from a lot of video jello. It does take decent stills though.
Also - I've updated the frame design to hold the mirror at the base instead of the top.