Jolteon @ Life Orb / Damp Rock / Heat Rock
Ability: Volt Absorb
Timid Nature
EVs: 6 HP / 252 SpA / 252 Spe
- Thunderbolt / Thunder
- Weather Ball
- Volt Switch
- Rain Dance / Sunny Day
Gen 8 did Jolteon a major disservice by removing Hidden Power and Signal Beam from its movepool. This left it only with moves such as Hyper Voice and Shadow Ball, all of which are nowhere near adequate enough coverage options to meet the demands Jolteon has as an Electric-Type. Therefore, Jolteon has become a relatively bland Electric-Type with little more than decently strong STAB options to its name, ironically making it offensively similar to how it was back in Gen 1. However not all is lost. Though it's true that it remains limited on weatherless teams, Gen 8 nevertheless gifted it with the move Weather Ball; It's an attack that becomes a 100 BP pseudo-STAB move (factoring weather) while in Rain or Sun, and with it Jolteon can see a new lease on life offensively by becoming a weather-reliant Pokemon. A boosted Weather Ball is stronger than Thunderbolt and has very respectable power when boosted by Life Orb. Between it and its STAB, Jolteon can be very difficult for your opponent to switch into safely; It gets better overall coverage in Sun than it does in Rain, as Grass-Types can resist the Electric/Water combination that Jolteon uses. Despite this, Rain in contrast lets Jolteon use Thunder instead of Thunderbolt. Not only is it stronger than Weather Ball itself, it also carries a nasty 30% chance to paralyze that can potentially cripple most switch-ins attempting to resist it. This goes in-hand with the fact that Thunder is made even more spammable by virtue of Jolteon absolutely demolishing most Ground-Types with a Water-Type move. Most Ground-Types are safe switches to Jolteon in neither Rain nor Sun, so Volt Switch in general becomes much more effective. It allows Jolteon to either pivot or preserve itself until its foes are more sufficiently weakened. Honestly, this set tends to demonstrate that Jolteon's worst offensive shotcomings have always been related to the limitations set by its STAB, and it's nice to see what it can do with those restrictions removed.
Jolteon should absolutely carry its Weather-setting move of choice in its last slot in order to either set up weather for its team in a pinch and/or prevent itself from becoming walled. I must confess that while I have used both the Sun and Rain versions of this set to good success, including within Smogon's PU, I have only ever used Life Orb variants of the set and never the Rock variants. I can't swear to the effectiveness of those versions of this Jolteon, but on the other hand, because Jolteon is blazingly fast and carries Volt Switch. I think it's perfectly clear it's nevertheless a good candidate to use for manual Rain or Sun. For sure, in the experiences I had playing these sets, there were definitely times where a would have rather had extended weather. So if you don't like Life Orb, I would definitely consider giving it a shot.