Goldvein Hydra ability did not trigger.
Had a 3 counter hydra and my opponent did a 'Nowhere to Run' -3 to kill my Hydra.
My Hydra did not give me treasure equal to it's counters, nothing triggered.
How this is a never ending issue with things not triggering can only be laziness from developers.
You must not have to assign elaborate triggers to every card, you must just select what triggers apply, and someone isn't doing their job right when it's the click of a button.
Staff deliberatley not donig their job right, means they get to stay on the books, getting paid to fix the issues they caused.
If devs do a good job, there job is done and they get fired.

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Rezzahan#77802 commented
Or you could learn to read, and the rules of Magic.
"When this creature dies, create a number of tapped Treasure tokens equal to its POWER."
Making the 3/3 Hydra into a 0/0 not only kills it, but also makes it create 0 treasures, as that was its power when last on the battlefield.