What would be verbiage I could use on my product that I am making as an accessory to another product who I have a licensing agreement with?

If you have a licensing agreement with ABC LLC, first and foremost, I would encourage you to review the license and see if the terms of publicly disclosing the licensing the agreement are discussed. Often, a licensor has specific language they want you to use and any variation on that language could create a breach of contract issue. That said, there is no magic language that is appropriate. More elaborate language might be useful if you are trying to sell your product off of the goodwill of ABC LLC (e.g., Official Licensed Product of ABC), whereas if you are only looking to make it clear that your product will fit/accessorize with the ABC toy, something simple avoids overshadowing your brand (e.g., Licensed by ABC LLC).  If you are an exclusive licensee, you may want to insert that 'exclusive' term in there as well, as it lets consumers know you don't have a licensed competitor.