If it feels like there are a lot more giant skeletons around these days, you're not imagining it.

What began as a viral novelty just six years ago has become a Halloween staple, and a growing line of business, as big-box retailers have responded to demand with an expanding array of towering monsters each fall.

"In 2020, Skelly's debut really was … the genesis of these fully molded structures that people could put in their yards," said Tyler Pelfrey, a manager of brand communications at Home Depot.

What followed was a retail arms race of increasingly elaborate creatures — undead horses, zombie velociraptors — with shoppers hauling home 85-pound boxes of oversized bones that might not fit in the trunks of their cars.

The decorations aren't the only thing expanding.…