I have an old sony universal remote, the rm-v15. I opened it to get to the pcb, and a strange nasty smell came out of it. Is there anything I should be worried about? Any hazards used in old remotes?
You could have a leaky battery; you don't want acid all over your skin. There will be trace amounts of the heavy metals found in all electronics manufacturing.
And because remotes are handled so much and are often full of skin cells and food traces, you could be smelling mold spores.
Wear gloves, ventilate, and proceed. You should be fine as long as you don't lick anything!
That was the magic smoke. It will not come back by itself. Remote is generally safer than other components that may use high voltage. Battery could be an issue, also get rid of anything leaking.