Fulhelmknight

Huh, I've been playing it wrong this whole time. Not sure why.

"Once, while this card is face-up on the field, you can negate the attack of 1 of your opponent's monsters. If this card destroys a Defense Position monster your opponent controls by battle, you can Special Summon 1 Level 4 or lower "X-Saber" monster from your Graveyard."

Note that Fulhelmknight does not specify that it has to send the monster to a specific place, much like Blue Thunder and friends. This means that, as long as it destroys a monster by battle (which is determined during damage calculation), the effect can be activated (at the end of the damage step like one would expect) even if Fulhelm was destroyed after doing so, such as by Ryko.

I was treating it as though it functioned like Goyo or Shura even though I knew the text was different. ._.

...so it's a smidgen stronger in that it doesn't need to remain face-up like the above two do.