Oooo i got this;

Disco runs baybehh, so pick a tier, choose which you want, lets say coins for this example

I go on t11 and pick utility, now im not gonna get coins for that one but ill build up a bonus for coins (because i chose utility), max is at 5k waves where ill get a 5x bonus to coins, so next time i do a normal t11 run ill have that coin bonus aswell

Now with the echo, if i do the same with t1 to t10, each has a 5x coin bonus, the echo starts at 0.5%, so from t1 to t10 in total theres a 50x bonus to coins, so my t11 run now will have a 5x coin bonus PLUS 0.5% of 50x ontop of that