Hi,
is there any reward for completing all challenges? I mean besides satisfaction. I already got 10 gold medals but with some challenges I have big problems and some of them are just too annoying.

Also, do I have to pick-up time bonuses in final challenge? I am able to finish it quite easily but even my best time is about 30 seconds short of gold. Is it just matter of fighting faster or is it because I was ignoring time boni?

hey, as someone who actually beat all challenges on gold there is not much for it. You get 1 costume for each 10 gold, silver and copper which are quite neat and ofc 100% compleation of El Inferno..

If it comes to final stage, your target is to get to the exit the shortest route u can go, in other words u don't need to explore whole stage, just rush to the end. Pick-up bonuses are good if u re wasted too much time on dead-end path, nothing more.