An easy way to create a simple lightsaber in AE is to use the "Beam"-effect, track the clip that you want to composite the saber into and then link the tracking data to the Beam-effect's "Starting Point" and "Ending Point". But how do you do this with a custom lightsaber, created in another composition? I thought it would be as easy as tracking the clip and then linking the tracking data to the position of two Puppet Tool-pins on both ends of the saber; I was wrong. Doing this results in a weird bend of the custom saber. I knew there are plugins, but this feels like it would be achievable without plugins.
Just download Video CoPilot's fantastic (and 100% free!) plugin Saber. It does more than just lightsabers, so you should have it in your arsenal anyway; it's incredibly useful for all sorts of energy effects.
It's sort of silly to self-limit to only native effects when there's a free tool that does exactly what you need.