1. if you clone a joker, then the cloned joker has a different back than the real one

2. Madness can't destroy eternal jokers but it does still get the +x0.5 mult

technically, the cloned joker always has red back, but non-cloned jokers have the same back as your deck

Madness also can't destroy itself, but the +x0.5 mult is applied before the destruction process (unlike with Sacrificial Knife) so it's not stopped by failing to go off

maybe the strongest two joker setup is a madness and an eternal Joker Stencil