As stated in the trailer, Harvester is based on the mode of the same name from Quake III Team Arena.
Every frag spawns a skull in the middle of the map. You have to collect the enemy team skulls and bring them to their base.
There are 21 arenas and 17 heroes available in Harvester. One DPS hero is randomly chosen at the beginning of the match and assigned to all players. Skull carrier's Ultimate ability and mobility skills get banned until the player scores or dies. This includes both passive abilities like Wall Climb or Glide and active abilitites like Combat Roll or Ice Wall.
At some point of scripting, I realized that Echo won’t be able to use the ultimate, so I gave her a new one. It's OP AF, but once again it’s a reference to Quake. Her new ultimate is called Kamikaze. Once Echo reaches 100% of ultimate charge she can initiate the self-destruct sequence, which will cause her to die, but create a big blast and take with her all the enemies that happened to be in the blast radius.