Let's get some new discussion on this forum. Tell me if I'm wrong, because I'm new here.
Don't use this:
Dugtrio @ Focus Sash/Choice Band
-Earthquake
-Stone Edge
-Reversal/Aerial Ace
-Sucker Punch
Why it's outclassed:
Dugtrio used to be one of the best revenge killers in the game due to it's ability, Arena Trap and it's blazing speed. This allowed Dugtrio to trap and kill opponents at its leisure. Sucker Punch was the icing on the cake, allowing it to defeat faster, frail pokemon (i.e. Alakazam, who has the same base speed and is weak to Sucker Punch). Focus Sash Reversal let it keep going once it would have seemed to be dead, and the now-200BP move had great coverage. Unfortunately, it now has severe problems. 35/50/70 defenses are below abysmal, leaving it prone to fainting from even neutral hits all the time. Here is a demonstration of how weak it its:
252 Atk Adaptability Feebas Waterfall vs. 4 HP / 0 Def Dugtrio: 220-260 (103.7 - 122.6%) --
guaranteed OHKO
Here is it being OHKOd by a Pokemon with 15 base attack, with no power boosting item, and a Jolly nature.
The power creep currently going on does not help it here.
Even worse, with the advent of Prankster, a Prankster Will-O-Wisp utterly destroys it. Both Banette-Mega and Sableye can run this. It weakens it's attack power hugely and breaks it's sash. Because it is a physical attacker, foul play shreds it too.
4 Atk Mandibuzz Foul Play vs. 4 HP / 0 Def Dugtrio: 213-252 (100.4 - 118.8%) -- guaranteed OHKO (assumes Dugtrio is Adamant)
It's ability, Arena Trap, also has two huge catches:
1. It can be traced by Pokemon like Porygon-2, who can trap and OHKO it.
2. Most important, all of these Pokemon aren't trapped by Arena Trap or hit by a STAB Earthquake: Flying Pokemon, Levitate Pokemon, Shed Shell Pokemon, VoltTurn users, and Air Ballooners.
To further compound it's issues, it has a weak base 80 attack stat. That is 5 points better thank Blissey's special attack, to give you an idea. It is weak to priority ice shard as well as aqua jet, and other priority attacks (Bullet Punch, ExtremeSpeed, Sucker Punch in particular since they are physical) wreck it as well.
252+ Atk Choice Scarf Mamoswine Ice Shard vs. 4 HP / 0 Def Dugtrio: 252-296 (118.8 - 139.6%) -- guaranteed OHKO
252+ Atk Life Orb Adaptability Crawdaunt Aqua Jet vs. 4 HP / 0 Def Dugtrio: 411-484 (193.8 - 228.3%) -- guaranteed OHKO
252+ Atk Choice Band Technician Scizor Bullet Punch vs. 4 HP / 0 Def Dugtrio: 280-331 (132 - 156.1%) -- guaranteed OHKO
Instead, use this:
Wobbuffet @ Leftovers/Focus Sash/White Herb
-Counter
-Mirror Coat
-Encore
-Destiny Bond
Why it's (so) much better:
One reason Wobbuffet is much better than Dugtrio is because of how useful it's stat spread is. High HP and low defenses make CounterCoat damage spectacular, and Destiny Bond carrying over a turn if you are slower makes the low speed less of an issue. It is remarkably hard to OHKO. If it max invests in the defense stat that you hit the hardest, just forget about it:
252+ Atk Choice Band Technician Scizor Bug Bite vs. 252 HP / 252+ Def Wobbuffet: 486-572 (83.2 - 97.9%) -- guaranteed 2HKO after Leftovers recovery
If you use U-turn (which does 64.7 - 76.3% max), what ever non-ghost comes in will get shredded. If adamant choice band Scizor uses U-turn on a max defense and HP Wobbuffet, switches into Blissey, and the Wobbuffet uses counter, the Blissey will be OHKOd 100% of the time.
Remember how I talked about the problems that Pokemon switching out of Dugtrio's Arena Trap give Dugtrio? Wobuffet doesn't care about these. It can CounterCoat Voltturning, and Pokemon that switch out bring in a new victim.
Encore gives you a free switch in on hazard setters, spinners, defoggers, set up sweepers, and more. Here's a special, nearly fool-proof trick to get rid of set up sweepers who switch into you if you have full health.
-Use Destiny Bond. They will have to use a non-damaging move if they feel like surviving.
-Encore that non-damaging move.
-Enjoy your free switch-in.
(As a final point, Dugtrio is more used than Wobbuffet, by a margin of 22 spots on the ladder and is used .26% more)