What would a cross-breed between a Giant and a Troll look like? And one between a goblin and an elf? [on hold]

Given that a cross breed between man and Giant has happened (Hagrid'd parents) in the Potterverse, despite it being highly non-viable, isn't it more probable to expect a cross-breed to have occurred naturally between Giants and Trolls, which are more comparable in size etc.? And similarly for goblins and elves, given that a cross breed between humans and goblins is known to have occurred (somewhere in the ancestry of Professor Flitwick)?