Bibarel

[A_man13]

#400 Bibarel
Normal/ Water
Simple: The effectivness of all stat modifications is doubled
Unaware: Foe's stat modifications are ignored

Mega-Beaver

Bibarel @ Leftovers/Pinch Berry
Simple: Impish
216 HP/40 Atk/252 Def
-Curse
-Amnesia
-Quick Attack
-Super Fang/Waterfall

Description+EVs+Options
Amnesia puts your SpD 624, Curse gives you 480 Def and 432 Atk. That's only 4 Atk lower than Azumarill. Super Fang lets you chip away at defensive walls until Quick Attack deals superior damage. Waterfall is also a good option for another STAB move.

Bibarel can take a physical hit before it Curses, but a special one will usually leave it too weak to do much else. After you set-up though, you're practically impenetrable. Rest+Chesto berry is your only reliable recovery option. It also rids you of annoying status effects your foe may use on you after you set-up. The beaver is slow, so make sure you Rest at the right moment.

Bulkier Beaver

Bibarel @ Leftovers
Simple: Impish
252 HP/252 Def/4 SpD
-Curse/Defense Curl
-Amnesia
-Toxic/Yawn/Stalling move
-Rest

Description+EVs+Options
Pair this up with some entry hazards and you'll be walling/PP stalling for eternity. If you really want to use an attacking move, Charge Beam is a nice option to get your SpA stat up to 302. That's about average at best. A second Charge Beam boost will get you up to 458, a threatening number. EVs are for maxed out Defenses. Because Curse gives you +2, while Amnesia gives you +4.

Firing the lazur

Bibarel @ Salac Berry
Simple: Modest/Timid
252 SpA/252 Spe/4 HP
-Endure
-Charge Beam
-Ice Beam/Surf
-Grass Knot/Surf

Choose your nature depending on what you want to outrun. The modest beaver after a Salac boost either ties with timid Azelf or outruns it by one point. I have no idea how rounding works in Pokemon. The Charge Beam strat is explained in the above paragraph.

Counters
Phazers. The first set doesn't deal with status/repeated hits/super effectives that well. The second set usually only gets to see the light of battle once before it becomes useless. Bibarel isn't that hard to defeat since it's 3 weaknesses are all pretty common.