CommentStreams:Ce5ab2e8f0552cde0681d009d745f0a8

you need  at least  1250 keys to open a golden coffer.

1250 keys = 125 fights at boss 21 = 125 x 20 silver = 2500 silver = 5 stone coffers = 1 golden coffer.

And to get  1250 keys  to open 5 silver coffers and then 1 golden coffer, with 3 keys per fight, you need 416 fights.

If you get the keys at a location that is 12 energy per fight, that is 416 fights x 12 energy = aprox 5000 energy. That is almost 1650 gems. That is per one golden coffer.

If you want 5 extra golden coffers, multiply by 5 the above.