Well, I have a female Sawsbuck that needs synthesis as an egg move, which it is going to get from my leafeon. Since leafeon learns synthesis at level 33 and it is currently at level 29; if I put my Sawsbuck and Leafeon in the Day-Care together, will the baby Deerling have no synthesis as an egg move until Leafeon turns to level 33? Or will it continue to have no synthesis?
Your Pokemon must know the move in order to pass it down.
If the male doesnt know the move yet, the baby wont learn it either.
But once Leafeon knows Synthesis, the offspring is 100% able to get it as a egg move.