Had a feeder goldfish punk/live with it's intended predator puffer for months.. that puffer would eat other feeders but it would avoid this 'special' goldfish.
I have no limit on mixing large cichlid with small tetra, barbs and live bearers, and plants that conventional wisdom says never. I am selective though on mixing only mild temper frontosa, Severum and acara with robust tiger barb, breeding heart tetra and sailfin molly, along with tough texture java fern, Anubias and sword plants. I am growing out a blue angle fish and pearl gourami to adequate size before introduction to the mix. I like mixing slow moving big fish with active schooling small fish in plants they can hide and seek.