"B.E.S.", short for "Bacterian Empire Ship" as well as known as "Giant Battleship" (巨大戦艦Kyodai Senkan) in the OCG, is an archetype of Machinemonsters based on the bosses of the Gradius series. They were used by Lorenzo in the Yu-Gi-Oh! GX anime, as well as by Nathan in the Yu-Gi-Oh! Tag Force games.
"B.E.S. Big Core" was previously known simply as "Big Core". Since "Boss Rush" has not been reprinted in the TCG since "Big Core's" name was changed, "Boss Rush" specifically mentions "Big Core" as well as "B.E.S." monsters.
The main strategy of any "B.E.S." Deck is using the effects of "Boss Rush" and "B.E.F. Zelos" to Special Summon "B.E.S." monsters as beatsticks and overwhelm the opponent with a destruction-proof force of battleships.
All of the "B.E.S." monsters share the same gimmick: they enter the field with counters on them. They cannot be destroyed in battle; instead they lose one of their counters at the end of the Damage Step whenever they battle, and will only be destroyed if they have none to remove. In addition to this, all "B.E.S." monsters are Level 5 or higher, so they rely on being Tribute or Special Summoned.
"B.E.F. Zelos", aside from being of paramount importance for any sort of plays this Deck tries to achieve due to the plethora of effects it grants, is also the number one card to start the game with. Since it searches "Boss Rush", it allows the player to set up a rather ideal board in the first turn consistently. Both "Terraforming" and "Planet Pathfinder" can help fetch "B.E.F. Zelos" and one should consider playing them at max capacity.
"Boss Rush" is part two of the standard "B.E.S." board. For the drawback of locking you out of Normal Summons, it fetches "B.E.S." monsters from the Deck during the End Phase in case any was destroyed during the turn. Note that multiple copies of "Boss Rush" can simultaneously search and Special Summon "B.E.S." monsters. However, "Boss Rush" is not only a recovery tool: the player can use "Dark Hole" or "Interrupted Kaiju Slumber" to clear the field, then proceed to Summon back reinforcements during the End Phase. Furthermore, "Limiter Removal" also triggers "Boss Rush" while transforming the battleships into a deadly force during the Battle Phase.
One detail that a "B.E.S." player should be aware of is how the monsters actually acquire their counters: the newer monsters (namely "B.E.S. Big Core MK-2", "B.E.S. Big Core MK-3", and "B.E.S. Blaster Cannon Core") get 3 counters upon being Special Summoned; the rest of the monsters only get counters upon Normal Summon, which means they will enter the field with no counters if Summoned via "Boss Rush" (unless "B.E.F. Zelos" is also on the field, in which case they get 1 counter).
"B.E.S." can be combined with a number of other archetypes, depending on what strategy the "B.E.S." player tries focus on. "Cyber Dragon" is a potential candidate to join forces with, giving the deck access to another Special Summonable Level 5 monster in the eponymous "Cyber Dragon", as well as some tech choices in the Extra Deck like the "Cyber Dragon Nova" and "Cyber Dragon Infinity" combo, or a plethora of Fusion monsters like "Chimeratech Megafleet Dragon". "Interrupted Kaiju Slumber" invites the idea of playing "Kaiju" monsters, most of the "B.E.S." monsters should be able to just run over the Kaijus that remain after they were used to get rid of more dangerous threats. "Infinitrack" also poses to be a worthy ally: The Infinitrack monsters in the Main Deck clash with "Boss Rush" if Normal Summoned, but due to the high levels of the "B.E.S." line-up, they allow for a consistent Summon of any Rank between 7 and 12 with relative ease. Additionally, "Infinitrack Anchor Drill" is able to search for both "B.E.S. Covered Core" as well as "B.E.S. Blaster Cannon Core", helping the deck with potential consistency issues. An "Infinitrack" engine allows for a number of Extra Deck monsters as potential playmakers in "B.E.S.", from "Galaxy" Xyz monsters to cards like "Number 9: Dyson Sphere".
As mentioned before, "B.E.S." is incredibly reliant on "B.E.F. Zelos", so any card negating or destroying it will hinder the deck.
Cards like "Acid Rain", "Magnetic Mosquito", and "System Down" have the potential to shut down the deck completely, since the archetype consists entirely of Machines.
Also, since they are Machine Monsters, they can also be used as Fusion Materials for an opponent's "Chimeratech Fortress Dragon".
