Plus and Minus, while being completely worthless in single battles, has quite a good use in the double/Triple battle metagame.
Minus:If another pokemon has Plus or Minus in the battle currently, Special attack increases by 1.5x
Plus: If another pokemon in the battle has Plus or Minus also, The user'd Special attack increases 1.5x
Users of:
PLUS:
Plusle
Klink
Klang
Klinklang
Mareep
Flaafy
Ampharos
Klink
Klang
Klinklang
Mareep
Flaafy
Ampharos
Minun
Klink
Klang
Klinklang
Electrike
Manectric
Klink
Klang
Klinklang
Electrike
Manectric
As you can see, there are some decent pokemon that can benefit greatly from Plus and Minus, most notably Manectric, and Ampharos who, in combination with a boost to their already impressive Special attacking stats(105 and 115, respectively) can tear quite a few holes into teams. Plusle and Minun, the pioneers of the ability also gain some use as well, being able to improve their below average 75 and 85 special attack stats. Klinklang however, benefits less, as it has the worst Sp.Attack of the group, a measely 70.This doesn't mean it can't be used, however in most cases it is outclassed thanks to it's far better attack stat.
COMBONATIONS
Manectric
Life Orb/Choice Scarf/Choice Specs
Timid
252 Sp.A/252 Spe/4 HP
Flamethrower/Flame Burst
Thunderbolt
Hidden Power Ice
Protect/Switcheroo
Ampharos
Choice Specs/Life Orb
Modest
252 Sp.A/252 HP/4 Spe
Power Gem/Protect
Thunderbolt/Protect
Signal Beam/Focus Blast/Protect
Hidden Power Grass/Protect
This takes advantage of plus/Minus's top attackers, boosting their impressive Special attack even higher. On Manectric, Flamethrower is the move of more power, while Flame burst hits both your opponents pokemon(while it usually only does a little, it does break sashes/Sturdy) Thunderbolt is for STAB, while hidden power ice is simply the common coverage move. The last Spot relies on Manectrics Item. If carrying a life orb, Protect is the best option, while if carrying a choice item, Switcheroo is the better option, being able to trap an opponent into a move.
On Ampharos, everything again relies on item, if using a life orb, feel free to replace any moveslot with protect, being vastly useful in doubles. if using Choice Specs, however it would be best going with 4 attacking moves. Thunderbolt is again STAB, while Power Gem gives you coverage over Ice and Bug Types. Focus Blast also covers Ice, as well as Rock, and Dark, the superior choice over signal beam, however Signal beam offers better accuracy, and Hidden Power also covers Rock types as well. HP Grass is used for various Ground/Non-Rock Types that would otherwise completely wall both pokemon, except from hidden power. mainly important is using on pokemon such as swampert or gastrodon, who are immune to Thunderbolt, and also easily shake off any damage done to it by hidden power Ice. HP Grass offers a nice counter to them.
Unfortunately, Should you feel you would prefer to not use Manectric, so if needed, can be replaced as such:
Plusle/Minun
Focus Sash/Life Orb/wide Lens
Timid
252Spe/252Sp.A/4 HP
Nasty Plot/Fake Tears
Sing/Protect
Thunderbolt
Helping Hand
Plusle and Minun have their uses after all it seems. however with 40/50 base defense, they aren't going to take many hits, So You can survive with Focuss Sash, use Nasty PLot to boost up, or Fake tears to weaken your opponent, then use Helping hand for super boosted attacks/spam thunderbolt until you die/spam sing/protect to survive as long as possible. Sing is used to try in an attempt to put a foe to sleep, keeping you slightly safer for the next few turns. Prtotect simply keeps you alive so your partner can abuse the Plus/Minus boost.
All in all, Plus/Minus are very underestimated abilities that, if unprepared for it, which many teams aren't, you can easily take out several members of a team with ease.
OTHER STRATEGIES:
-Plusle and Minun both learn entrainment, so
Plusle/Minun
Focus Sash
Timid
252 Spe/252Sp.A-or-HP/4 HP-or-Sp.A
Entrainment
Protect
Thunder Wave
Thunderbolt
Entrainment a special sweeping pokemon, increasing it's special attack, and taking a hit, leading it to use it's sash, then try and support with T-Wave and Stall with Protect, in order to survive as long as possible to have your partner keep the boost. posible partners include Zapdos, Latias, Salamence, or any other Special sweeper really. can also partner with pokemon such as Regigigas, Who has a dominant attack, and decent special attack that can be brought to special sweeping potential with Plus/Minus boost, leading to a potential mixed sweeper.