Before the establishment of the first gates magic linked to other planes would not exist.
This includes all undead (they didn’t exist) most necromancy spells, all shadow spells and many more depending on the description of the spell. When in doubt consult with one of the enlisted DMs.
Magic that utilize extradimentional space is not effected, but etheral, shadow, astral and other planes are.
Before the fall of the egg the plane should be considered a magic dead area. The dates on which each permanent gate is opened will be provided shortly (it will not be before the year 32036)