Voted "No Viable Echo." None of the echo options are particularly related to Wario himself (aside from Mona/9-volt, who absolutely would not work as farting, chomping, twerking fighters).
Nominations for Snake: There's actually quite a few that work here. Since Solid Snake himself is -literally- a clone, there's no less than 4 characters who share his DNA in some fashion:
* Solid Snake (MG1/2, MGS1,4, presumably the one in Smash)
* Naked Snake/Big Boss (MGS3/5/PSP, MG1/2 antagonist, Solid's genetic donor/father)
* Liquid Snake (MGS1 antagonist, Solid's blonde twin clone-brother)
* Solidus Snake (MGS2 antagonist, Solid's aged-looking clone-bother, uses a completely different twin-katana fighting style, though, not a great Echo.)
* Venom Snake (MGS5, surgically-created doppleganger of Big Boss)
Additionally, there are couple of major characters who could use a similar Close-Quarters-Combat fighting style as him, and all are shown to be proficient with firearms/explosives:
* The Boss (MGS3 major character, Big Boss's mentor, almost a mother-like figure, seeing as how Robin/Corrin/Villager don't have any issue having female alternate costumes, the change from a male base graphic model to a female one should be trivial as far as Echoes are concerned, similar to Marth/Lucina.)
* Raiden (MGS2/R, Solidus' adopted son and essentially Solid's protege, originally used the same skillset, but he does focus on the katana in more recent games for some variety)
* Revolver Ocelot/Liquid Ocelot (MGS1-4 antagonist, Naked AND Solid Snake's eternal 'rival', more known for gunplay, but an accomplished operative in his own right)