There's a listing, "Swamp Thang," under the Spoof Comics heading on page 132. It doesn't list the source. The Swamp Thang card is unnumbered, undated and bears no indication of its origin other than some text describing the subject. It's another one of the random inserts you could get with the serial-numbered (out of 4000) "Trading Card Edition" of the "Amazing Heroes Swimsuit Issue" #5 (Amazing Heroes August, 1993).