FFA and Experimental
If a player uses a skin, the color of their cell will still be visible on its outline, and on its ejected mass. But a player with a premium skin has an outline that goes with that skin, but not the ejected mass. Ejected mass sticks with the outline color on the cells in mobile though. However, you can change the settings to see no skins and colors at all.
Players' cells constantly move in the direction of the cursor (with a slight delay due to latency). Smaller cells move very quickly, while larger ones move much slower. Note that if a player is in control of multiple cells, they will all move towards the cursor, allowing a player to draw their cells together and help them to merge.
Pressing the space bar allows a cell to split into two parts of equal size. If a player has multiple cells, typically each cell will split. This mechanic functions in that each original cell remains in its previous position, loses half of its mass, and a new cell with equal mass is projected from its position in the direction of the cursor. The maximum number of cells a player can have is 16.
Pressing the W key will eject a small lump of Mass, which behaves similarly to a food pellet. Any cell that is 1% larger than the ejected mass can consume it, including the cell that ejected it. This mechanic is especially useful in Teams mode, as it can be used in order to feed a teammate to allow them to consume a larger cell on an opposing team. Be aware though that although the ejecting cell loses 18 mass, the resulting lump will only give 14 ass to the cell that consumes it (a fraction of the Mass is lost).
Cells grow by either collecting pellets, or by consuming smaller cells or viruses. Cells lose mass over time, at a rate of 0.2% of their mass per second. This means that if you don't consume anything, you would lose half your mass in 5 minutes and 47 seconds. This also means that cells of certain size can no longer sustain their mass solely through pellets. They must instead consume other players' cells or viruses to maintain their size, or grow further. There is a setting to see the mass of your cell(s).
All cells have a mass limit before forced to split. The maximum mass limit for a cell is 22,500 mass. The maximum mass for the entire player is 360,000 (22,500 × 16). If a player consumes more mass while being this big, the mass will instantly vanish. Cells have a maximum split limit which is 4 times, resulting in 16 cells.