HA! I had to burn all my clovers right at the beginning to get enough damage output with max level Stones but this build was able to burn through the first 15 waves! I'm sure I won't last much longer though ;)
edit: Got Centurion too! Magma + Maxed Stones + lots of Boulders seems to be a nasty combo for a lot of bosses.
Nice! Yeah Hard-mode with endless is definitely a real challenge with the adjusted enemy health levels, I usually enjoy starting with Earth+Water to get the benefit of the slow from the splash tower, and the ice tower can be critical to get through some of the swarmy waves.
Here's my most recent setup I used to beat king slime without any clovers!
Glad you are having fun!
And finally, beat Mother in Endless on Harder! It took me a lot of tries but I'm proud to say I used my work day well ;) 
Well, I think I just about capped out what I could accomplish on this run without re-thinking my strategy. 
I bet I will revisit this and see if I can beat Mother++++ with a different layout sometime... Suffice to say, fun game!
