Hoopa
General Strategy
Hoopa has two primary movesets with very different goals. You should select your moveset depending on both your preferred playstyle and also how much you trust your allies. Items, especially Experience Share, should also be used based on what you expect from teammates.
Trick and Shadow Ball is the easiest moveset to master, while also being the safest to play with unknown allies. This moveset allows you to be very aggressive towards the opposing team because it combines stuns and frequent auto attacks with shielding for you and a single ally. The movement speed bonus that comes immediately after using Trick can help you and your allies escape from a difficult battle.
Trick is an exceptionally good pocket move that gives yourself and your ally a sizable shield and bonus movement speed. It also doubles the amount of Shadow Balls that are fired, with both being capable of dealing full damage if hitting different targets. Your auto attacks will also fire from both yourself and the tricked ally, increasing your damage output and stun capabilities. Learning how to "rescue" an ally with trick is an important aspect of this character. The level 10 upgrade also provides a huge amount of healing for you and your tricked ally by recovering 25% of all damage dealt.
Aiming both of your Shadow Balls at the same opponent will allow you to immediately stun them. This move has a surprising amount of range and can be cast quickly so feel free to use it on fleeing opponents to secure a KO. It also passes through and damages all enemies within its path, so fire it into crowds whenever possible.
Hyperspace Hole and Phantom Force is a moveset that relies on your teammates to utilize portals to heal themselves and is the go-to moveset for high level, competitive 5 stack play.
Hyperspace Hole allows yourself and your allies to teleport back to the home base, fully heal their HP, and then teleport back to the initial location. It also connects goal towers on opposite sides of the map, allowing for fast rotations (you cannot go back to the base to heal when they are used this way) across the map. This move is potentially countered by Pokemon that have displacement moves (shoves, grabs, and throws) so be sure to estimate the cooldowns for opposing Pokemon that have them. This move is risky to use in solo-que because you cannot force allies to use the portals, leaving you with a somewhat low damage move that doesn't do much else.
Phantom Force is a move that gives Hoopa the ability to teleport a short distance and shove enemies where it emerges, dealing a hefty amount of damage in the process. After you teleport, you can optionally move back to your initial location by pressing the move button again. As such, this move can be used to bait out and dodge your opponent's attacks. This move can also be paired up with Trick to gain new functionality; if you Trick your ally before using this move, they can portal back to your initial location and regain a significant amount of health.
Items
Muscle Band (Highly recommended for all movesets)
Muscle Band is an excellent item for Hoopa, especially if you are using Trick to pocket your allies. Auto attacks that come from yourself or a tricked ally can both deal 3% remaining HP damage if they hit separate targets.
Rapid Fire Scarf (Highly recommended for Trick moveset)
This item also works well if you time its activation window for after Trick has been used on an ally.
Experience Share (Recommended when you know your lane partner)
Hoopa does not evolve so it can use experience share more safely than other lane supporters. If you don't know your lane partner, it will often be better to use an item that increases your offensive or defensive capabilities.
Choice Specs (Recommended when you don't know your lane partner)
While Hoopa does not have the highest special attack stat, this item can increase your chances of securing lane farm in the early game while also slightly increase damage and shielding that you can provide for allies.
Energy Amp
Hoopa has one of the most powerful Unite moves in the game in terms of pure utility (moving all allies across the map is amazingly useful on its own) and it also provides a very high damage Psybeam attack which can hit multiple opponents. Hyperspace Fury also deals a lot of damage and stuns within a small area.
Slick Spoon
This item is useful for movesets that do not include shadow ball, which already reduces your opponent's special defense stat. Spoon will increase the effective damage from Phantom Force and Hyperspace Hole, which can be combined for a powerful secure on wild or opposing Pokemon.
Path strategy
Top and Bottom path (Recommended)
Either of these paths work so long as you are paired with an offensively capable Pokemon. Your goal in either path is to help allies secure neutral farm while providing stuns (via Astonish) to aggressive opponents.
Central area (Not recommended)
Hoopa has a decently fast clear time but is best played while supporting another ally in a path. It is possible to help a jungler clear faster if you are using Experience Share, although you should only do this if expecting an opposing jungle invade.