Promos for major events are not legal unless they have been printed in a set that is legal for that event.
For example Gencon will use
Mage Wars Core Set
Forcemaster vs Warlord Expansion
Conquest of Kumanjaro Spell Tome Expansion
Druid vs Necromancer Expansion
Forged In Fire Spell Tome Expansion
If you use the
Spellbook Builder you can see if a card is legal for an event.
At a local level it is up to the T.O. or Judge to announce if they are allowing promos or not for each event. I tend to let players know as soon as I announce an event if I am allowing promos or not. 95% of the time the answer is no.
PS: This has been asked and answered before please try to search before posting next time.
Never mind I just searched and it did not show up.