I'm considering returning to pokemon with the NU tier (partially because it has a lot of my favourite pokemon and partially because I've always had the impression that NU has an awesome community) and I'd appreciate some miscellaneous info and tips.
Which pokemon are especially dangerous? Which have to be played around carefully rather than outright countered? What are the most relevant speed tiers? Which team archetypes are popular?
I played a lot of BWUU and a tiny bit of BWNU, plus some XYUU and some early ORAS OU.
Which pokemon are especially dangerous:
Hey man welcome to NU. Honestly "threats" come in such a large variety, and we do our best to keep them in order through a grading system known as viability rankings here -
http://www.smogon.com/forums/threads/oras-nu-viability-rankings.3523692/
it should give you some sense to the threat makeup of the tier.
Which have to be played around carefully rather than outright countered:
Again this somewhat depends on your own team and how it is prepared to match with certain threats. For example, offensive teams don't typically pack outright counters, but instead pokemon that can remove each others checks / counters. IDK how to word it, but it ultimately depends on how large a threat is to a specific team.
What are the most relevant speed tiers:
While we really don't consider speed tiers by relevancy, in NU 110, 95, 80, 65, 50 are all pretty crowded.
http://www.smogon.com/forums/threads/oras-nu-speed-tiers.3515004/ thats the full list of all relevant speed tiers.
Which team archetypes are popular:
I'd definitely argue Bulky Offense and Balance reign supreme in the current metagame due to the massive amount of bulky hard hitters that saturate hte metagame, although NU's versatility allows other playstyles such as HO, Stall, Weather, etc. all to succeed when played correctly.
Hope this helps, welcome to NU.