The Invincible attack is an attack that Mario or Luigi temporarily gain after they pick up the Star Power-Up item. and becomes Invincible Mario for a brief time until this Power-Up wears off.
As presumed from the name of this attack type, nothing can harm Mario/Luigi except lava or poison. Mario and Luigi may kill other invincible foes such as Dry Bones and Thwomp. In this form, the Mario/Luigi glitters and possesses the colours of the rainbow, (However, this colour change is mostly seen in modern Mario games and spin-off games.) can run faster and jump higher.