Your Constitution ability score increases by 2 (with no upper limit)

You have received a blessing, or a special boon, from a very powerful creature.  Likely, you have accomplished a momentous task for this entity, or they are pleased with how you have displayed great courage or selfless humility, or you have simply done something truly amazing that catches the attention of both gods and mortals.  The reasons for being granted a blessing or boon are many.  Remember, however, these special considerations can be taken just as easily as they are given.