Shadow is like Wario? Do i need to remind you that wario is in the game? And that he has his own games which did fairly well. And that hes like, an important nintendo character now (well maybe i dunno)
Tails isnt a pure sonic clone, neither is shadow. Tails attacks with his tails, shadow attacks with his weapons and psychic powers. Tails doesnt have blasters to use in his moveset, but whats this? Shadow HAS guns and blasters.
Tails has a plane? Shadow has a motorcycle and a car.
Tails is just a sidekick, i doubt he has accomplished anything up to the calibur of shadow. Tails is only meant to be a sidekick, and that is how he is portayed in the games. If any sonic character was to make it in, it would have to be shadow, and plus rivals make good characters in smash
You clearly missed the point of the Wario argument, so I'll make it more plain. Yes, Wario's in Smash. He debuted in the third game. You know who was there from the very first game? Luigi. You know - the
sidekick. I don't think Wario was even considered for the first Smash like some other characters were.
Yes, Wario's games do well. That has nothing to do with this, so I have no idea why you brought it up. If it was relevant, though, you can't say the same about Shadow, because we all know how
his game turned out.
Tails
does have blasters can use. He has a very large number of devices, in fact, that were invented by him. His intelligence is said to rival Eggman's. Check the wiki, if you don't believe me.
Some of his attacks/ inventions that he could use:
http://sonic.wikia.com/wiki/Magic_Hook
http://sonic.wikia.com/wiki/Energy_Ball
http://sonic.wikia.com/wiki/Flick
If you want an example of what his moveset could be, just look at how he plays in SSF2. In fact, three of his moves from that game come from the pages I linked. The Tornado in this game makes a perfect Final Smash, and it even functions like Snake's Grenade Launcher.
It doesn't matter about accomplishments or whether he's a sidekick. Those are just empty excuses. They don't take away from who he is as a character. Of course, you're underestimating just how important Tails is. He's been an integral part of the series since long before Shadow was around.