Let me tell you the tale of the fabled "EMC Apple". Consumption would grant complete immunity to every attack for 10 seconds, as well as a regeneration II effect for 60 seconds and restoring two hunger points. This apple is special and has two stages. The first stage will only be usable when below full hunger, the second is most powerful, grant Imunity to all attacks for 20 seconds instead. Afterword, the apple is a normal golden apple.
I dont think the promo should be just an op item, some of my favorite promos have been cool items like the cupid's bow and the labor bench. I think having just a super op item cheapens the fun effect of the event or milestone.
How about the emc apple having only one use. Gone forever. And just really rarely, make it crafts with 8 gold blocks and a golden apple (teir 2)
I think it should not be just another promo. Who said there even HAS to be a promo for it? I think that there ought to be something small and humble that has some attribute that makes it non tradable. Something like what FDNY suggested.
The only difference between my cake idea and the cake idea you just thought of is that yours only has 100 uses. You almost exactly copied my idea.