Nidhogg, Generaider Boss of Ice — Ruling

Effetto 0

The effect that states you can only have 1 face-up Nidhogg, Generaider of Ice on your field is not classified as an Ignition, Trigger, Quick, or Continuous Effect.

This card's effect that negates the Special Summon of an opponent's monster is a Quick Effect. (It does not target, and cannot be activated during the Damage Step.)
Tributing a "Generaider" monster or Wyrm monster in your Monster Zone is the cost to activate this effect.
This effect can only be activated when your opponent performs a Special Summon without starting a Chain, such as a Synchro Summon, Xyz Summon, Pendulum Summon, Link Summon, etc. (It is not an effect that you activate by chaining to effects that Special Summon, such as Polymerization.)