>>46234241>buff them through abilities and moves instead of changing their core statsTrue but you don't need to make them signature moves for that.
>Beedrill had twinneedle, Raticate had super fang/hyper fang, Gastly line was the only ghost type, Dratini line was the only dragon type, etcThat's fair. Though besides Beedrill all of those were loosened up eventually. This illustrates both the main aspect that I enjoy about signatures and the one that I hate about them the most.
On one hand, when they get distributed widely in ways that fit with the pokemon that get them, it redeems the original exclusivity they had to them. This is great. On the other, when you have something remain with one specific design for as long as Twineedle, you know you've gotten a stupidly specific meme on hand. This is like Tsareena's Queenly Majesty or Frosmoth's Ice Scales. Both would require them to make yet another design with those specific qualities (dominant queen monster, ice butterfly/moth), which is greatly restrictive creatively. The best signature moves are always available for other lines at least two gens later. Strange Steam and Spirit Break have great potential for further distribution, should they happen to make more lines with mist/steam based weird powers or aggressive, violent fairy types.
