Ejecting mass is an ability that is used to send 18 mass to cells. On the browser version of the game, "W" is the default key to eject mass, while on mobile press the button with a shooting cursor below the two cells button (split button). On the mobile version there is also "macro ejecting", which is a hack that allows much faster ejecting.
Ejecting will cause all of the players cells (above 35 mass) to launch a small pellet of mass towards the cursor, similar to splitting. The ejected mass can be eaten by any cell that is 21 or 22 mass and above. Cells lose 18 mass per ejection; however, the mass of the ejected piece is only ~72% of that. Consuming the mass only gains 13 mass.
To be able to eject, each cell needs to have at least 35 mass.
Ejecting can be used to transfer food between the cells of a player or to donate mass to allies. It can also be used to create more viruses. As shown in the picture, ejected mass has an angle of spread, meaning that Viruses created may veer off course by ~20 degrees. This spread can be lessened by getting closer to the Virus, although this may also increase the risk of accidentally consuming it.
A good but tough strategy is to eject mass into a virus until it splits, then move to the new virus and split it, so you will have a triangle of three viruses, which you can squeeze in between them to hide inside the virus fort. Big players will be too afraid to try to eat you, because they might hit a virus and split into multiple pieces. If you were big enough, you could consume the small pieces of the cell.
If ejected mass is left alone long enough, it may function as a spawn point for a new player. They will have the same color as the ejected mass. (eg. if a player spawns from the mass Chrozick ejected, they will be red because Chrozick is a red cell.) Skins do not effect the color your cell will be if you spawn from mass.
Players should keep in mind that any cell (even enemies) can consume the ejected mass, so it is important make sure that the target cell is close to the ejecting cell.
Ejecting can be used to speed up a player's cell as a less loss-heavy tactic than splitting. By ejecting and recollecting, you can move faster. However, you will lose mass and are prone to being eaten.
If you eject mass into a virus, the virus will consume the mass and get slightly bigger. If you eject 7 pellets into a virus, a new virus will be shot out in the direction of the last ejected pellet which was fed to the virus, and the original virus will immediately shrink back to 100 mass.
In experimental, shooting viruses immediately moves them. They don't split. They move ~3 grids per ejected mass shot at them. Spawner viruses get bigger if you eject mass into them or put a smaller piece of mass into it. However, they don't move. They only get bigger. Any mass you put into it it turns into pellets which are outside of the virus. You can eat these pellets. It will keep decaying until it's back to its original size.
Teaming and Communication with Ejecting
Most of the players in Agar.io know that if they give some mass, they either want to have a team, or bait smaller cells to come closer and then split kill them. This doesn't only happen in Party, but also in other game modes.
Ejecting mass can be used strategically in team mode to slow down other cells, help an allied cell engulf an enemy, or to prevent an allied cell from being eaten. It can also be used to communicate with teammates, such as telling them to split on an enemy cell, then feeding/pushing the piece to eat the cell.