The second Earth-Twelve Plastic Man first appeared in Plastic Man (DC, 1966 series) #1 (November-December 1966). His origin was revealed in Plastic Man (DC, 1966 series) #7 (November-December 1967).
This version of Plastic Man appeared in the following issues: Plastic Man (DC, 1966 series) #1 (November-December 1966) through #4 (May-June 1967), The Inferior Five (DC, 1967 series) #2 (May-June 1967), Plastic Man (DC, 1966 series) #5 (July-August 1967) through #10 (May-June 1968), The Kingdom (DC, 1999 series) #2 (February 1999)