(Equipment, Auras you control, and counters are modifications.) If the creature you control is an illegal target as Signature Slam tries to resolve but the creature you don't control is still a legal target, each modified creature you control (which may include the target creature you control if it's still on the battlefield) will still deal damage equal to its power to the creature you don't control
Remember, characters cant be exerted to sing on the same turn they are played (unless the card says otherwise)
It was indeed a very good card at the time, it would not be at all unfair to call Eternal Witness the original Snapcaster Mage
My prediction may have missed the mark, but it wasnt by much, as sapphire lands itself in the Top 3, just behind amethyst and ruby
Both cards have their own grading communities and dedicated collectors pursuing PSA 10 copies
Both cards are Sprigatito 016/159