There are many weapons and tools to help you survive in The Anacrusis, but some of them have unique interactions with the various enemy types that aren’t noted anywhere in the game. For example, you can’t expect your Pulse shield to knock away the massive Brute — it’s just too bulky. Many grenades have unique properties as well, so here is what the Vortex Grenade does in The Anacrusis.
The Vortex Grenade, when picked up, grants you two uses of Vortex. Vortex creates a swirling, uh, vortex wherever the grenade lands. This vortex can vacuum up smaller enemies, dragging them into the center dealing periodic damage the entire time before a final explosion sets off, dealing more damage. This is an excellent Horde clearing grenade — and there doesn’t appear to be a hard cap to the number of units it can affect.
However, this grenade does not impact Brutes. Again, Brutes are simply too big to move around or be affected by things like Vortex, Pulse, and Shield effects. Vortex can affect some of the smaller specialty aliens like Gooper and Grabber, but because they are highly mobile, and Vortex has a very small window where the effect works, you may not be able to hit them with it reliably.