X can't be 0.
Target spell's controller exiles it with X delay counters on it.
At the beginning of each of that player's upkeeps, if that card is exiled, remove a delay counter from it. If the card has no delay counters on it, the player puts it onto the stack as a copy of the original spell.
If Ertai's Meddling is used to copy an arcane spell that had effects spliced onto it, it will create a spell with all of those effects. That spell's controller will not be able to splice additional effects onto the spell, since they did not re-cast the spell and instead simply put it back onto the stack.