The Sixty Deaths of Solomon Grundy!

Superman and Swamp Thing

The Swamp Thing wants to analyze Grundy, in hope of a cure for himself. So--he cannot let Superman take him away! He allows Grundy to defeat Superman--aids him, even--then leads him away.

Grundy has decided that the two are friends--"No! You are friend! You and Grundy are different together! Can't kill friend!"--and Swamp Thing takes advantage of this to get a skin sample to analyze.

Ultimately it turns out that the sewers are spawning copies of Grundy. Superman decides that these clones aren't really alive, and kills them all. Swamp Thing isn't happy with this plan, but can't communicate his disagreement before Superman rushes off to the killing fields.