I think the Strong Spheres storyline is the closest thing we have gotten to Shadow Pokemon in the anime.
1. Pokemon who are infected by laquium get overly aggressive and become stronger. The bond with their trainer is also weakened and sometimes they stop listening to their trainer. Shadow pokemon also got aggressive, their power was artificially enhanced and the door to their heart was closed as a result of an undisclosed scientific experiment.
2. Both are distributed to the public. The company Exceed sold strong spheres in mass so that trainers could use them on their pokemon. In the Colosseum games, we also see regular trainers using shadow Pokemon (although it is not specified if they bought them in the same way as strong spheres).
3. Shadow pokemon, as well as pokemon infected with laquium are more willing to attack people and not just other pokemon.
4. In the anime pokemon affected by laquium can be battled with in order to snap them out of the effects once defeated or Terapagos can absorb the laquium to heal them. In the games, shadow pokemon do need to battle to eventually be purified (although in the games there are other methods to help purify them as well), but my point is that in both battling helps them snap out of it eventually, although the artificial engineering of shadow pokemon is much stronger and durable than the effect of strong spheres.
5. In both instances a legendary or mythical pokemon has the power to completely reverse the effects of the affected pokemon. In the anime is Terapagos, in the games is Celebi (colosseum only).
