The King of the dark knights, The KnightHero Swordius-Arthur is one of my favorite spirit which I like to put it in many kind of purple decks, because of its very high BP and a fact that it is a burst, so it could be summon at no cost.
Swordius-arthur effect starts from the burst effect , which is a burst summon. This helps players avoid paying the highest cost in the world of Battle Spirits, 12. Also, it could be used as a tower defense, due to the fact that Arthur only need 1 core for level 1, but already has 10000 BP. That's not all, it can revive your spirits with immortality in your trash and summon them without paying the cost, so players can create an army of dark knights and make a great combo. It is good with braves too, since it has a level 3 effect when braved, it could send one core from an opposing spirit to their owner's reserve.
Cards that are perfect to combo with this card are spirits with immortality, preferably The HollowEmperor Netherd-Baaral and The MagicalPrincessDeity Geraldy. But to help afford their first cost, add some cards that allows you to discard your own cards, like The Canyon Where Sage Lives , Danse macabre or The KingSnake Quetzalcoatl. Braves are preferred too, like The KnightSnake Pendragon and The HolySwordDragon Ex-Wyvern. With Pendragon, you can send 2 cores total from any opposing spirits to the void and the reserve respectively, they can be different spirits.
To counter this spirit, you might need the white attribute "returning" efforts, or some blue cards that can destroy opposing spirit under a condition, like The IronHero Saigord-Golem. Some brave-destruction red cards like Double Blaster or Burst Flame are OK too.
-Very high BP.
-Burst summon effect.
-Summon a spirit with Immortality from your trash at no cost
-When Braved, send one core from any opposing spirit to the void.
-a high cost of 12
-needs a life to activate the burst
I like the artwork a lot, it resembles a fully armored king ready to battle in a war, holding a great sword, similar to the British legend of the Excalibur.
I give this card 10 to 10.