DPPt/HGSS This is an in game team...

Teach a Timid Jolteon RETURN? That is awful advice - Timid lowers Jolteon's Attack which is already terrible to begin with. Do your research and make sure you know what you're talking about before posting advice Feralagtr - it'll be a warning next time.

In any case, this seems like it's trying to be a competitive team as well - for in-game it's probably fine as it is, but a bit of polish usually goes a long way, so lets start:

- Empoleon's EV spread has been mistyped since you can't go 252 EVs in three stats. In any event, Drill Peck and Earthquake will be of little use here since Empoleon's Attack is a bit crap with a Modest Nature. I'd drop Drill Peck for Grass Knot and possibly go Flash Cannon for your final slot.

- Gliscor's fine and dandy as he is.

- Double Team is usually banned competitively, so if you do decide to make the transition to competitive, keep that in mind. Otherwise, Attract will see somewhat limited use overall since it only affects the opposite gender and can leave Jolteon open for a turn, which usually results in it dying. Signal Beam is a great alternative if you have access to move tutors, otherwise Charge Beam's power boost and great ability to revenge-kill opponents is a good alternative.

- Gardevoir may struggle to set up Reflect if she's up against anything that packs decent offensive power, but otherwise I'd still consider it viable for the good synergy it provides alongside Calm Mind.

- Tangrowth really doesn't want Naive nature or Speed training since it's slow as a slug no matter what you do to it. Brave or Quiet is probably best for this set since it'll boost your offensive power a bit more, and the Speed EVs should go to HP instead. Moveset is OK overall.

- Froslass will prefer to have Shadow Ball over Ominous Wind to avoid its PP levels dropping to zero, or Thunderbolt to provide that and better coverage as well.

Overall good and interesting ideas - this is definitely a team you'd want to test a bit to see if any of your ideas work. They have the potential to work well, but obviously that means nothing if they don't actually perform as well as you'd like in practice.