Hmm well ur setup deals with semi-agressive to mild fish so it's kinda hard to find some badass fish for ur tank. Plus we are reaching the maximum capacity point before its overcrowded (I mean it's up to u if u don't mind but I think just filled with a space is a cooler aesthetic) so my final recommendations are maybe another eel (black spot or spiny like u had before but research about those sizes and compatibility with ur fish and the peacock eel) or a African leaf fish maybe some cool loaches like khuli or yoyo or clown if u have room they get big.