For aesthetics, you can add PlayObjectAnimation("Devil", "happy", ONESHOT_STILL);

function DevilF
Trigger(OBJECT_TOUCH_TRIGGER, "Devil", nil);
MessageBox("/Maps/SingleMissions/Test_Skriptov/Devil.txt");
AddHeroCreatures("Christian", 3, 20);
PlayObjectAnimation("Devil", "happy", ONESHOT_STILL);
end;

Trigger(OBJECT_TOUCH_TRIGGER, "Devil", "DevilF");

Added 1 minute ago
If anything is unclear, ask, and I'll try to answer :)

Added 5 minutes ago
PlayObjectAnimation("Devil", "happy", ONESHOT); this is better

Added 27 minutes ago
Here's a tip: it's better to edit scripts in the Skripts Editor; you can also create text files there, which will simplify the process

Added 6 minutes ago
function DevilF
Trigger(OBJECT_TOUCH_TRIGGER, "Devil", nil);
MessageBox("/Maps/SingleMissions/Test_Skriptov/Devil.txt");
AddHeroCreatures("Christian", 3, 20);
PlayObjectAnimation("Devil", "happy", ONESHOT_STILL);
end;

Trigger(OBJECT_TOUCH_TRIGGER, "Devil", "DevilF");

SetObjectEnabled("Devil",nil);

Now everything is correct, it should be

Added 31 seconds ago
function DevilF
Trigger(OBJECT_TOUCH_TRIGGER, "Devil", nil);
MessageBox("/Maps/SingleMissions/Test_Skriptov/Devil.txt");
AddHeroCreatures("Christian", 3, 20);
PlayObjectAnimation("Devil", "happy", ONESHOT_STILL);
end;

Trigger(OBJECT_TOUCH_TRIGGER, "Devil", "DevilF");

SetObjectEnabled("Devil",nil);

Now everything is correct, it should be