Kommo-o

Great League: 3.5 / 5

Kommo-o is a unique addition to Pokemon Go as a Dragon/Fighting type. With a double weakness to Fairy-type attacks, this becomes very concerning against "Charmers" as well as the popular Azumarill. Its bulk is very similar to that of Dragonair, which isn't spectacular but still viable. An aggressive moveset with Dragon Claw spam pressure and STAB Close Combat threat is no joke however, and Kommo-o's offensive capabilities gives it a lot of play against various Pokemon. Its pre-evolution Hakamo-o sports slightly more bulk, but has access to the much weaker Brick Break instead of Close Combat, which overall is a downgrade. 

Ultra League: 4 / 5

In a league without common Azumarill getting in its way, Kommo-o challenges much of the meta with its fast-paced moveset. Dealing neutral spam against most opponents while also having an answer to Steel-types that resist Dragon Claw enables a lot of flexibility for offense. Opportunities for farming down an opponent with low HP is a very scary scenario if Kommo-o can take advantage of it. Just keep in mind that Kommo-o isn't a tank and can't take prolonged battles. 

Master League: 3 / 5

Since Kommo-o can't reach Close Combat fast enough to outspeed Dialga in an even fight, it's better to consider limited formats like the GBL Premier Classic instead of open Master League. Doing so also avoids other unfavorable and powerful legendary Pokemon such as Zacian and Lugia who have significantly more stats and typing advantages. Compared to other non-legendary Pokemon, Kommo-o somewhat falls behind in stats, and this is shown in certain matchups like against Dragonite who has a higher ATK stat and therefore priority to Dragon Claw. However, access to the powerful Close Combat lets Kommo-o stand out in its unique way, especially against Steel Pokemon.

Since the Season of Light update, Kommo-o faces major competition with Dragonite, as the latter's new access to Superpower greatly overlaps with Kommo-o's niche.