Start Loop While : [{EXP:1=1}] Equals '1'
Begin Text Compare : [{EXP: {MOUSESCREENX} < 250 AND {MOUSESCREENY} < 250}] Equals '1'
Begin Boolean Compare : [~doneOnce] Equals False
Write '[Blue] This will run once' to log
Set Boolean [~doneOnce] to True
End Condition
Else
Set Boolean [~doneOnce] to False
End Condition
End Loop
You can use the condition builder rather than the "{EXP:}" token, but you'll have to store the cursor position into variables if you want to avoid using "{EXP:}" altogether(and if you're using it anyway, you might as well do both checks in one go, I recon).
Do note that in multi-monitor setups, any monitor to the left of the main monitor will result in negative coordinates, so you'd have to add a ">= 0" check as well.
You can have the loop check a variable, if you want the ability to stop it at will(Either from another command, or with some additional logic, when the same command is executed a second time).