Skarm I'd start considering after Celebi/Zapdos/Gengar, tbh. It's always been good, but its super-high usage throughout most of its existence is mostly in reaction to other dominant things (usually Snorlax), so it's hard for me to see it in the top 5. Definitely worth considering for 6-10, though, because of its consistency as a premier defensive Pokemon and the breadth of stuff it defends against in each generation. Also, Celebi can be counted for GSC because, for quite a while, it was perfectly legal and was on a lot of dominant teams. Older people might be able to comment better on it. And no way Starmie cracks the top 5. It was nominally OU in each gen, but was a far cry from dominant in any metagame except probably for early RBY. The aforementioned C/Z/G trio hits a top 3 spot in at least one metagame, a level of dominance Starmie has never really hit. Finally, the Zapdos thing was an exaggeration. It's definitely nominally OU. I was just making the point that it's mediocre compared to other OUs. To use stuff we've discussed before, it's somewhere between GSC Ttar and DPP Snorlax in RBY usefulness. A position that actually kind of detracts from an argument of its dominance, even though it is nominally OU.