| I haven't messed with sC for a long time, but I'm pretty sure this is an easy trigger:
[Conditions]
Current Player Brings Exactly 1 Unit To Beacon
[Actions]
Subtract 1 Minerals From Current Player
Wait 1000 Milliseconds
Preserve Trigger
I'm pretty sure this is correct. You can, of course, adjust the milliseconds and the mineral subtraction.
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