This workflow keeps responsibilities separate: the mask defines geometry, Glow handles light, and the source video remains independent.
Prepare the moment that needs the outline
Use Freeze Frame, Reverse Speed or retiming only when the shot design calls for it. First decide where the outline should appear; do not make speed changes a mandatory part of the effect.
Draw a Polygon mask
Trace the subject with a Polygon mask. For a line, disable solid fill and use Border Width. Fewer unnecessary points make animation and tracking much easier.
Separate the bright core from the Glow
Create a sharp bright line first, then add Glow. If you need a richer halo, a second softer Glow is usually easier to control than pushing one node to an extreme.
Animate Length and Position
For a drawn-on effect, animate the visible segment length and position. Time the movement to the shot rather than simply going from 0 to 100 over an arbitrary number of frames.
Add controlled variation
A small brightness pulse, color drift or gentle Glow modulation can make the line feel alive. Keep this variation slower than the main reveal so the contour does not look like it is flickering.
Merge over the source and inspect the edge
Composite the line over the original image and zoom in on corners, intersections and places where the Polygon leaves the subject. For moving objects, track or animate the mask.
Key takeaway
Clean neon outlines come from simple Polygon geometry and separate control over the core line, glow and reveal animation.