Don't forget Loki has other kids... Like Odin's horse and I think Hel, the half Dead, is also a sibling... if I'm remembering things correctly.
Which means you can have random phone calls from Billy's mysterious sister. The clingy one, she does have a realm you can't leave without her
permission and only Loki (and Billy in this case) have ever managed to escape. Give Billy something to ramble on about... the clingy sister that keeps trying
to get Billy to visit... but Billy knows that Billy can't leave Hel's realm unless Billy brings something spiffy to bribe her with. Presents, and
promises of more next time, are half the reason Billy can get out.
Which means you can have random phone calls from Billy's mysterious sister. The clingy one, she does have a realm you can't leave without her
permission and only Loki (and Billy in this case) have ever managed to escape. Give Billy something to ramble on about... the clingy sister that keeps trying
to get Billy to visit... but Billy knows that Billy can't leave Hel's realm unless Billy brings something spiffy to bribe her with. Presents, and
promises of more next time, are half the reason Billy can get out.