The effects of Birthday Cupcake will stack with Candy Apple and Grail of Might, for a total bonus of +300 Health and +30 Energy.
Bug! Birthday Cupcakes were accidentally added to the list of items offered by Sheng Yi during Dragon Festival 2009. (He normally offers them only during Birthday Celebrations.) This was confirmed to be a bug, but the Live Team decided to leave it rather than release a new build to remove it.