Ghost replay
A translucent copy of an earlier lap that races alongside the player in time trials, unable to collide with anything.
Super Mario Kart already had one in 1992: the game kept your best lap and let it drive again as a pale shadow. It is a stripped-down replay system. Rather than inputs, most games store position and rotation a few times a second and interpolate between samples, because replaying inputs only reproduces the lap if the physics is fully deterministic — and it rarely is across patches.
Trackmania turned the ghost file into currency: leaderboards download the record holder's lap so you can chase it corner by corner. The same file gets used to vet suspicious records, which makes it both sparring partner and evidence in speedrunning circles.