Question

What level should I evolve my eevee into jolteon?

Answer 1

If this is for in-game use, then Jolteon's only good moves are thunder and thunderbolt. Thus, you should evolve it when you get a TM for one of those moves. If this is for competitive use, then you can evolve it whenever you want. None of Eevee's or Jolteon's level up moves are good in competitive battles, so it shouldn't matter what level or moveset it has when it evolves.

Comments

What about Thunderbolt? It's usually harder to get than than Thunder but when you consider the accuracy an heavy PP usage in-game, I would say it's better than Thunder.

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It depends on the game, I guess. I know that, at least in DPPt, thunder is cheaper.