The Adventures of Mustard Man – Chapter 5

Dear Justice League of America,
It is with much regret that I must decline your invitation to join your esteemed organization. Not only am I an ordinary person who lacks superpowers or technological wonders to simulate superpowers, but I am under exclusive contractual obligation to the Mustard Man Brand Mustard Company.
However, should the world be under attack by mustard-vulnerable alien invaders, much like the Martians in the “War of the Worlds” story were fatally vulnerable to the common cold virus, then please do not hesitate to call upon me through my numeric pager.
Regards,
Mustard Man
Enclosed: sampler package.