When this card is Summoned, declare different Monster Card Attributes equal to the number of "Disciple of the Forbidden Spell"(s) in your Graveyard. If this card attacks a monster that has a declared Attribute, destroy the monster with this card's effect without applying damage calculation.
And watch as they survive with Neos Fusion, Fuma or Shi En's effect and you lose a bunch of LP for no reason. Or they just Bacon Saver or Enemy Controller and attack over it. Or they just let you kill their thing and then attack over it.
I wasn't saying Shi En can negate Disciple. I was saying it can destroy another Six Samurai instead.
And yes, baiting those things out is a thing you can do. But there are also much better cards that can destroy things like Shi En or Brave Neos that don't require set-up. Why should I use Disciple over a card like Cipher Soldier, Golden Dragon Summoner, Snipe Hunter or Koa'ki Meiru Ice?
Combine with Needlebug Nest and Tribute to the Doomed to get the full effect.