You don't, Tails isn't playable in Sonic 1 because he wasn't introduced until Sonic 2. I'm sure you can find hacks of Sonic 1 that let you play as Tails though.
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In the real game no, because Tails wasn't introduced until Sonic 2. You can however use hacks people have created to play as Tails in Sonic 1. Try out this one on Sonic Retro, that allows you to do just that
Tails killed Sonic in self-defence because when Snively injected that formula into Sonic's arm, it turned Sonic evil. If Tails hadn't have stabbed Sonic, he would have been choked to death, so it was a lose-lose situation, anyway. And I'm sure that the last thing Tails wanted to do was kill his best friend. I'm pretty sure that Tails killed Sonic because he had to. Sonic is the fastest thing alive, he always wins, and he can become Super Sonic if he has the Chaos Emeralds. Tails had to kill Sonic because if Sonic is a bad guy then everyone may as well kill themselves. No, he didn't want to, but Tails can't technically be choked, as he has no neck.
Yes. Just go 2 options, and select the character you want to play as: Sonic, Tails, or Sonic and Tails. NOTE: If you are just as Tails, you cannot go SUPER SONIC, however there is a cheat to go SUPER TAILS, but you need both Sonic and Tails to do this.
sonic tails knuckles
first, you put game genie code of hyper sonic and 80 rings.Then, choose tails and do a double jump.