I bet it was a 25/17 with dive, after diving it was 50, and he used 2 basilisk bloods to make it 57.
Either way, he would have had to buffed the creature up, and used a bunch of TU's and fallen elves don't ever seem to improve upon a creature it simply mutates them, so you mutating 10x and making the creature better just sounds foolish.
Besides, this is about the WEIRDEST thing, not the most powerful.