Zeraora, a Mike Tyson level puncher.
Overview
Zeraora is an excellent carry for the whole run. It hits hard, has unmatched speed and godlike coverage. Even if its mega exists, it doesn't needs it to work well (although this is a very big boost). It needs Ice punch, if you don't have it, Zeraora isn't a viable full-run carry.
Strengths
Its biggest strength is its speed. With 143 base speed, it's guaranteed that almost nothing will be faster. It hits also fairly strong, with 112 Atk (and colossal 157 if mega). Pure electric is a nice typing, and it learn very good moves. Its passive Iron Fist is very useful, as it's boosting Ice Punch, Power up-Punch, and during a small portion of the run Thunder Punch.
Weaknesses
Its bulk is fine but not great, even the mega doesn't reinforce it at all. It can take a hit, but not two, especially against ground moves. Also, even if it has good moves, they do not hit the hardest, even if its passive boost them a bit. And it's costing 7 (5 if reduced), a bit expensive.
Recommended build
Adamant is the ideal nature, it really doesn't need a +Speed nature. For the objects it's the usual with carries (aka gave it everything). Map is recommanded, with it just go in water biomes and cause carnage.
Moves & abilities
Its moveset will be formed of an Electric STAB, 2 coverage moves and a boosting move. The Electric STAB will be changed through the adventure. It starts with Spark, then learns Thunder punch, and finally Plasma Fists. The latter, in addition to hit very hard, can work with Zeraora's ability Volt Absorb, making Normal-type moves heal you. Ice punch is its first coverage move. With it, Zeraora now possess the iconic BoltBeam coverage, letting it hit almost every Pokemon with only these two moves. It's also its main response to Grass, Dragon, and especially Ground Pokemons. And it's boosted by its Passive. Fire Lash is the second coverage move. With it, no pokemon can now resist the lightning cat (well except Marowak Alola). Good base power even if not boosted by the Passive, and excellent effect by reducing the enemy's defense each time. Power-up Punch is my pick for the last move. It's a boosting move, designed to make Zeraora's other moves devastating. Even if it only has 40 base power, it's still boosted by Iron Fist, is super effective on a lot of pokemons, and is more powerful over time. Zeraora can try other moves. If you have the egg move Swords Dance, you can replace Power-Up Punch. Both are viable. As for Collision Course, I would not recommand it, unless maybe if you got the Mega, but else it needs a way to boost its Atk. Its moves also have the advantage of having a lot of PPs, a nice bonus.
Strategy
Pretty simple strategy (like practically the same I wrote for my Marshadow guide) : use Power-up Punch when Zeraora is send, until you can one shot everyone with all your moves. The biggest difficulties are gonna be luck-related : if your rival has Torterra or Swampert, and/or if the bad guys team are team Magma. (also be careful of ground-type gym leader, but don't wander in biomes with ground types and you'll be fine). Elite 4 ground-type member is also a risk. But Zeraora should stomp everything else in the game, except Eternatus. Well, precisely for Eternatus, it has very good tools, like Fire Lash, but it lacks the bulk to tank more than one attack (or even tank just one Eternabeam). If you have found a Multi Lens, maybe it can solo it, with combination of Fire Lash to reduce defense, Power-up Punch to boost Atk, and Ice Punch for massive damage. (You can also cheat and instant Master Ball)
Synergies
As a full-run carry, its best teammates will be cheap shinies to boost the shop. If you're afraid of Ground type pokemons, pick one that can effectively counter them. And also pick one that can easily defeat Eternatus if you think Zeraora cannot do it (I think without its mega it cannot, at least not reliably).
Tips for beginners
Prioritize super effective moves, or its Electric move if you're afraid to take too much damage by letting the opponent an opportunity to attack because you clicked Power-up Punch to boost the next attacks. If you're facing a trainer and you think this trainer will switch, click Power-up Punch, you'll get a free boost without taking damage.
Tips for advanced players
If you find a ground-resisting Tera shard, you can gave it to Zeraora (can't work if it has its mega thought).