Speedrun Mode is a special mode intended for competitive streamers who complete the game in a single sitting. It eliminates dialogue, cutscenes, and all randomized elements, as well as providing an on screen timer.
Secret Worlds are removed in speedrun mode making the Scissor Beam, Fat Beam and Heat Seeker weapons unavailable in this mode.
Health drop chances are changed in speedrun mode as there are now enemies that never drop health, always drop health, sometimes drop health, or enemies drop health when Trace is low on health.
An offical blog post by Happ detailing Speedrun Mode can be read here:[1]