ADV OU - often praised by many as a tier of balance, can be seen as a happy medium in between the drawn-out stalemates where players have on average 2 birthdays per game that plague GSC, and the offensive RainTurnSandDragVoltSunMagDonkey spam death-every-other-turn metagames of BW2. The purist's metagame has almost come to a standstill in its development. It has gone through many phases, fluctuating between an infestation with SkarmBlissClopsDolCuneFiller teams (and then Boah reared its head), TSS teams such as Superman, and CMspam and mole teams. Many cores, both offensive and defensive, have been around since cavemen walked the earth - you'd see many a prehistoric hunter-gatherer tribe dancing around a fire and singing gleefully about how Swampert and Flygon in conjunction allowed a team to cover Electrics universally, or mumbling about Curselax and Magneton while foraging for berries, or carving crude drawings of Metagross and Zapdos onto cave walls. However, some new cores have developed in recent times, expertly crafted by the smooth moisturised hands of excellent players such as M Dragon. Two such notable comparatively newer cores are the infamous Forretress Gengar PursuitTar core, designed to keep hazard control - helping Forretress keep its own Spikes up (Gengar spinblocks), and spin those of the opposing team away (TTar removes spinblockers). Fill the remaining three slots in your team with defensive juggernauts which fill the holes, and you have an all-singing, all-dancing ADV OU team. Another perhaps lesser-known core is the DoubleDognDug team style. The idea is to use CM Suicune and CM Raikou, along with Dugtrio (sometimes Adamant for Bliss when Suicune is Offensive nonSubCM), which can trap threats to the pair such as Roarkou, Heracross, and Jirachi. Add Exploders, cover weaknesses, and a team is born, forged from the mines of Isengard. ADV OU is a fun metagame to get into, and there are a wealth of strategies waiting to be explored.
Currently, over the past 3 or so months, Cloyster teams have dropped out of the meta again, partially due to the newfound ubiquity of Toxic Skarmory, which screws it over, in that now Spikes will go down against Cloy teams. CM Blissey is possibly the most common Blissey set among top players currently, and many a Blissey sweep is pulled off against unprepared teams. Due to the influx in Calm Mind Blissey, Curselax is gradually returning to its original position of being chosen above 4 attacks MixLax.
Currently, over the past 3 or so months, Cloyster teams have dropped out of the meta again, partially due to the newfound ubiquity of Toxic Skarmory, which screws it over, in that now Spikes will go down against Cloy teams. CM Blissey is possibly the most common Blissey set among top players currently, and many a Blissey sweep is pulled off against unprepared teams. Due to the influx in Calm Mind Blissey, Curselax is gradually returning to its original position of being chosen above 4 attacks MixLax.