South American giants with a defensive behavior nothing else does: threatened, they spin in place and kick backward with the rear legs, which are noticeably thickened for exactly that purpose.
M. robustum out of Colombia is the common one, red-legged and large. M. mesomelas from Costa Rica is smaller, cooler-running and considerably harder to source. Both want more humidity than a typical New World terrestrial and neither tolerates heat well.
mesomelas is the price story. It comes from montane cloud forest, it does not breed reliably in captivity, and it dies in setups kept at the temperature most keepers default to. Thin supply plus high attrition keeps it expensive and keeps it appearing and disappearing from the market.