Play applies the profile's mod list and starts the game through its loader. Direct Play (not a Steam or store URL launch) can start more than one instance, spaced by a delay, for local multiplayer: set both in the game's settings under Play (Instances and Delay seconds). Develop's Test starts copies on its own. A Heroic or Lutris copy starts through its own launcher, so the game runs in the prefix and runner the launcher keeps for it. In a BepInEx game whose bridge has a console, the Console tab takes commands. Skip the intro in Stardew Valley's settings skips the title intro. Start first in the game's Play settings starts SteamVR, or the ALVR dashboard (choose its program there; it opens SteamVR itself), before the game; a profile can turn it off to play a flat-screen mod. Launch options… in the menu beside Play opens the profile's own launch options: extra arguments for the game, a command prefix (for example gamemoderun mangohud) and environment variables; the prefix and the environment apply to direct launches only. Launch presets keep several sets, each a Play with choice in that menu.
On Windows, Steam's own Play starts SMAPI with the game's own Mods folder, not a profile. Press Play in Mortar, or use the profile menu's Add a desktop shortcut (Start Menu on Windows, launcher entry on Linux) or Add this profile to Steam (a non-Steam game; close Steam first).
After a crash
A card on the profile's Home names the likely cause, read from the loader's log (for Lethal Company also Unity's player log) and, when those name no mod, the game's crash dump. When the game died in native code the card names the module and offset; for Unity's player and the Windows system libraries Mortar then downloads that module's public symbols from Unity's or Microsoft's symbol server (only then, and only when online) and names the function instead.
- Most likely cause: <mod> shows the log line and the Stack frame or dump line. Disable it and play disables that mod and relaunches.
- Find the cause… asks first, then checks that the game crashes with every mod on, then disables mods in halves and relaunches until one is left. A library stays on while a mod that needs it is on. Dismiss hides the card for that run.