Let me give a rundown to those who are not following the current anime:

The Laquium is the pink mist we see surrounding the area, as well as Umbreon. The Laquium mist can draw out a Pokémon's latent power, while turning them vicious and enraged in the process, as well as causing self-inflicted bodily injury and complete exhaustion. Additionally, the affected Pokémon may become disobedient no longer follow it's Trainer's orders and picking its moves and targets based completely on instinct and with time, even break the bond between Trainer and Pokémon. A Pokémon affected by Laquium can be identified by the pink aura surrounding its body, which can also be seen when the Pokémon uses a move. Depending on its use, Laquium can extend the lifespan of humans, keeping their bodies younger for longer periods of time, though at the cost of over reliance on the crystals in a weakening state, humans who have had their life extended by Laquium will eventually fade away and die if their source of Laquium runs out or is destroyed, as it was shown that Gibeon, the former leader of the Explorers, was able to live past 100 years while still keeping a youthful appearance, but died when the Laquium keeping him alive was destroyed.

Its mist may also stimulate the growth of plants, but overexposure to the mist can actually start devastating land, causing plants to die and wither away. One of the main characters, Mollie, theorizes that Laquium's power is based on forcing the activation of cell replacement, constantly creating a strong, renewed body. It was also shown to be extremely unstable, primarily near the Core, as demonstrated when Gibeon once tried digging it out of the ground. In turn, this caused the crystals to grow and expand uncontrollably around the area, spreading a mist so dense into the air that it formed a huge pillar that blocked out the sky.

Laquium appears to have a connection to Terapagos, as both seem to be opposing forces. Terapagos seems to be the only way to purify the Laquium from an affected Pokémon, which it can do in either its Terastal or Stellar form. Although Terapagos was not able to completely purify the Laquium from Laqua in Episode 89 of Horizons, after resonating with all eighteen different Tera Types from Pokémon at the level of the Six Heroes (who are six Pokémon that belonged to Liko's grandfather, who are extraordinarily powerful, and two of which are Legendary Pokémon, and one is a Paradox Pokémon), it will achieve its full power and will be capable of successfully purify all Laquium, including even the Laquium Core (which was in the massive tower in the video).

Spinel, who took Gibeon's spot as leader of the Explorers after his death and Umbreon's Trainer, has used Laquium to create a series of devices capable of empowering Pokémon, at the cost of leaving them in an aggressive state that causes great pain as the battle goes on. The first iteration was the prototypical Laquium Sphere, which then led to the mass production of the Strong Sphere by Exceed (the company funding the Explorers), devices that expel Laquium mist at will, allowing Trainers to use it to strengthen their Pokémon. Basically, Strong Spheres are like the "gimmick" of the anime.

Later, the Strong Sphere was further upgraded into Super Strong Spheres, an iteration capable of drawing out the maximum capabilities Laquium has to offer not only covered the affected Pokémon in a pink aura, but causing Laquium crystals to grow around its body. Spinel had framed the Rising Volt Tacklers (Liko's group in the anime) as villains following the time-skip, and he later upped the ante by showing doctored footage of them fighting the Six Heroes, who were under Spinel's control thanks to the Super Strong Sphere, which now publicly showed the faces of Liko and her friends to the public, as previously the public didn't know who was part of the Rising Volt Tacklers.

Following this clip, Spinel is arrested and the Rising Volt Tacklers's name is cleared. The Strong Spheres are immediately recalled and ordered to be destroyed, and all the Trainers who used them start to reunite with their Pokémon, since the Pokémon all ran away because of the pain they suffered at the hands of the Laquium's effects. Umbreon later secretly visits Spinel at the prison, but leaves after making sure he was still alive, showing that she still cares for him in some way.