Slaking

Truant
This Pokémon does nothing every other turn.
Type Tier
Normal OU
Statistics
Min- Min Max Max+
HP
150
- 441 504 -
Atk
160
320 356 419 460
Def
100
212 236 299 328
SpA
95
203 226 289 317
SpD
65
149 166 229 251
Spe
100
212 236 299 328
Name Item Nature

Attacker

Choice Band Adamant
Moveset EVs
~ Return / Double-Edge
~ Earthquake
~ Shadow Ball
~ Focus Punch / Fury Swipes
4 HP / 252 Atk / 252 Spe

Predict and kill something. It's really quite elementary. Choice Band Slaking will nearly guarantee a KO, if you predict correctly. Return / Double-Edge for powerful STAB damage that will kill nearly everything that it is neutral against. Double-Edge can work with Slaking's titanic HP, and works even better if you have a Wish Pokémon on your team. Focus Punch for predicting things like Skarmory that will come in to ruin your fun. Shadow Ball for those annoying Ghost-types that are immune to your other three moves. Earthquake for what's left (Steels and Rocks like Metagross and Rhydon). Fury Swipes can hit enemies behind Substitutes, like Jolteon, Ninjask and Sceptile, who are a threat to Slaking, but only use with Magneton, otherwise, Skarmory walks all over you even more than usual.

Other Options

Slack Off. Don't use this unless you're playing around, though. Hyper Beam can be useful only in a handful of circumstances. It can kill Weezing in one hit and take a Suicune down if it has 90% HP or less, but these are very situational, making Return the best choice. Flail can be useful if your Slaking is low on HP, it's possible that it becomes more powerful than Return or even Hyper Beam. Don't put these options over Return even though they are all Normal-type, because Slaking needs his STAB Return badly. You should replace Focus Punch if anything, because all that is really good for is Skarmory, which you can use Magneton for.

EVs

252 Attack / 252 Speed / 4 whatever with Adamant personality.

Opinion

Very scary. You need to predict well to use it and it forces your opponent to predict against you to keep his team alive. Prediction wars will be assured. Watch out for Substitute and Protect though, because those ruin your fun.

Counters

Ghost-types can be really annoying if you can't predict the Shadow Ball well enough. Prediction in general is a good counter as well. Spikes will slowly eat you up and Protect users / faster Substitute users will make Slaking useless.

Why you shouldn't use Brick Break and Rock Slide on Slaking

I see a lot of newer players using Slaking, but many of them make the same common mistake over and over. They'll use moves like Brick Break or Rock Slide over Focus Punch. There is no reason for this. The moveset shown above (Return / Earthquake / Shadow Ball / Focus Punch) will deal with every single Pokémon in the game. If you predict them switching in something weak to Fighting, why would you need to Brick Break instead of Focus Punch? Predicting is a big part of Slaking, both when using it and playing against it, so expect lots of switches.

Let's take a look at Rock Slide first. What exactly do you need Rock Slide for? You have Return and Earthquake for Fire-types, Return and Focus Punch for Ice-types and finally Return alone will defeat all the Bug-types in the game with an OHKO, save Shuckle, who will be defeated by multiple Returns or Earthquakes. You might think you need Rock Slide for Flying-types, but what Flying-types won't you be killing with Return anyways? Here are some damage calculations for Slaking's standard moves against Aerodactyl and Zapdos (typical Flying-types) as compared to the damage output by Rock Slide. These damage calculations are using a Slaking holding Choice Band.

Slaking's Return vs. Above Average Defense Zapdos
Minimum Damage: 323
Average Damage: 352
Maximum Damage: 380
Slaking's Rock Slide vs. Above Average Defense Zapdos
Minimum Damage: 318
Average Damage: 346
Maximum Damage: 373

In fact, Rock Slide does even less to the Zapdos by a few points than Return. There is no point to waste a needed move slot on Rock Slide in this case. Both Return and Rock Slide will kill the Zapdos in a single hit, though.

Slaking's Return vs. Standard Aerodactyl
Minimum Damage: 228
Average Damage: 248
Maximum Damage: 268
Slaking's Focus Punch vs. Standard Aerodactyl
Minimum Damage: 447
Average Damage: 486
Maximum Damage: 525
Slaking's Rock Slide vs. Standard Aerodactyl
Minimum Damage: 449
Average Damage: 488
Maximum Damage: 527

Even Return will take away an 82% average of Aerodactyl's HP. Both Rock Slide and Focus Punch are about equal in damage and easily kill Aerodactyl, but without Focus Punch you'll be lost against Pokémon like Skarmory. The only advantage of Rock Slide here is if you switch Slaking into Aerodactyl, and then need to OHKO it as it attacks. Aerodactyl is rare, and isn't the best switch in for Slaking, anyway, and as such there is no reason to use Rock Slide when Return and Focus Punch will take care of all Flying-types equally as well.

For Brick Break it's much of the same. People believe they need this to defeat Normals, Rocks and Steels when Slaking's existing moves will get the job done with the same efficiently and can cover even more Pokémon. Let's look at Snorlax right now and compare the damage done to it by Return and Brick Break.

Slaking's Return to Average Defense Snorlax
Minimum Damage: 379
Average Damage: 413
Maximum Damage: 446
Slaking's Brick Break to Average Defense Snorlax
Minimum Damage: 373
Average Damage: 406
Maximum Damage: 438

On average they will do about equal damage. Earthquake and Focus Punch will do more to Rock and Steel-types than Brick Break will. It is common sense. The only advantage of Brick Break is to hit the extremely rare Cradily more than the three non-Focus Punch moves, but that is not worth it at all.

Newer players are obsessed with seeing the words "It's Super Effective" and don't bother looking at the damage powerful STAB moves will do, even at neutral damage. Against Skarmory, Focus Punch will do more damage than either Brick Break or Rock Slide mainly because of the Base Power. 150 as compared to 75 in both cases. Focus Punch will do double the damage in that case. When you are doing lots of damage, STAB means a lot more than "It's Super Effective" without STAB. Please don't use Brick Break or Rock Slide Slaking—it's not worth it.