Guild Wars 2

Im really new with the COF speed run and i realize every boss kill its guaranteed 15-20s + in the first run. How does it work if I do the run repeatedly will the reward (gold wise) still be around that amount or does it drop from 20s(1st run)-15s(2nd run)-10s(3rd run) and so on.

Thanks in advance.

Try it and find out

The silver from bosses is guaranteed.

The only thing that really diminishes from consecutive runs is the tokens that you get at the end.

Dahkeus.8243:

The only thing that really diminishes from consecutive runs is the tokens that you get at the end.

XP, Karma, and gold awarded at the end of the run are also affected.
See DR article :
http://wiki.guildwars2.com/wiki/Diminishing_returns

… and the illustration for DR rewards on the dungeon wiki page (bottom right):
http://wiki.guildwars2.com/wiki/Dungeon

It uses CoF to illustrate the principle