A team after 4 year-long break.

[Gitny]

Hey, I haven't played pokemon since gen IV, so I had a lot of catching up to do and I'd really appreciate some help with my teambuilding. Here comes!

Sharpedo @Sharpedonite
Jolly
Speed Boost
EVs: 252 Atk / 4 Def / 252Spe
- Protect
- Psychic Fangs
- Crunch
- Waterfall

I decided to try a Mega Sharpedo and build my team around it. No idea how if it works well in OU nowadays.

Serperior @Grassium-Z
Timid
Contrary
252 SpA / 4 SpD / 252 Spe
- Leaf Storm
- Dragon Pulse
- Giga Drain
- Taunt

Decided to use a contrary serperior as a wallbreaker for bulky water-types that counter Sharpedo. Never liked Life Orbs, so I deleted Leech Seed for the sake of Taunt and picked Grassium-Z.

Alola-Marowak @Thick Club
Adamant
Lightning Rod
252 Atk / 4 SpD / 252 Spe
- Flare Blitz
- Will-O-Wisp
- Shadow Bone
- Earthquake

Lightning Rod provides a nice counter to electric attacks aimed at Sharpedo, plus Shadow Bone is a nice fairy killer.

Klefki @ Leftovers
Careful
Prankster
252 HP / 4 Def / 25SpD
- Thunder Wave
- Spikes
- Magnet Rise
- Play Rough

Klefki is a spike support for Sharpedo. Went for Magnet Rise to eliminate another ground weakness.

This is where I'm stuck. Wanted to add a strict Def wall like Weezing, Haze is a nice move to wreck boost users. Gliscor was my other thought, but then again - won't my attack be a bit low overall?

Idea for Weezing:

Weezing @ Black Sludge
Bold
Levitate
252 HP / 252 Def / 4 SpD
- Explosion / Destiny Bond
- Haze / Clear Smog / Whatever
- Flamethrower / Thunderbolt (I'm inclined to the latter one, as Marowak covers fire type moves.)
- Sludge Bomb

 

[RebornFX]

I think you're in the wrong section bro. This is for VGC ( a doubles format), not OU. You probably just want to post this in the SM OU RMT section.

However honestly if this is your first time playing since Gen IV I don't think making a team is the best way of starting out again. I would play with a team from the RMT section that has performed well and just play to see what's common or at least to remember what certain things do (although Pokemon roles have almost certainly changed since gen IV). Read through their descriptions very thoroughly so you know their justifications for certai moves, though if you want you can alter them if you feel comfortable doing so.

And just so you know, Shadow Bone isn't super effective against fairies. Fairies are weak to steel and poison and resist dark, fighting and bug and are immune to dragon. Fairy attacks are strong against dark, fighting and dragon while are resisted by steel, poison and fire. I'm not sure if you knew that or not but I thought I'd clear it up.

 

[Gitny]

Oh, I'm terribly sorry. Lots of things had changed. I guess you're right by saying I need to read up on stuff and observe others first.

Cheers!