At the beginning of your end step, Gisela triggers, exiling it and Bruna, and returning them to battlefield melded into Brisela, Voice of Nightmares.
Because Brisela prevents opponents from casting spells with mana value three or less, and Gaddock Teeg prevents players from casting noncreature spells with mana cost equal to X or mana value greater than four, your opponents cannot cast noncreature spells.
Results
Opponents cannot cast creature spells with a mana value of three or less.
Opponents cannot cast noncreature spells.
You cannot cast noncreature spells with mana cost equal to X.
You cannot cast noncreature spells with a mana value greater than three.