Assuming that the beast somehow eats souls, I did some research. There's a limited number of "beasts" in classical mythology that can feed on souls: Wraiths are just stereotypical undead that eat people's souls or emotions. Succubi and incubi can consume souls, but they're not appropriate for a game played by little kids. Energy Vampires are vampires that feed on energy or souls like normal vampires drink blood. Interestingly enough, the three headed skeleton could be Cerberus by the gate. In Dante's Inferno, he had three human heads (like the skeleton). Dante's Inferno also lists that Cerberus devoured intruders who tried to pass and caused torment for the gluttonous souls he guarded. Dragons are also symbolically linked to gluttony, explaining the other skeletons. Even though everything matches up, I don't think this idea is plausible. If Cerberus was the skeleton, though, playing music (how?) or throwing earth or a cake at the skeleton (how?) might do something. There is also Ezekiel 22:55, which links evil priests with devouring souls and destroying families, but I think its another wrong solution. So I would guess that the beast is an energy vampire or a wraith. It could just be something random, though, if Jagex is unorthodox. Seriously, though, has anyone tried using the "great magic" skull scepter there?