Li Shenron
Legend
So apparently now the "official" rule is that if you have a negative Constitution modifier and roll for HP at level up, your maximum HP might actually decrease.
While this might make for an occasional interesting story, it is likely the result of an oversight when writing the rules, and in fact Mearls (who may not always remember the RAW, but clearly knows the RAI) have previously always said there is a minimum of +1 HP when levelling up.
Not that this will have any real implications on anyone's game, considering that few players ever play a low-Con PC, and if they do they will probably now ask the DM for permission to gain average HP at level-up instead of rolling.
While this might make for an occasional interesting story, it is likely the result of an oversight when writing the rules, and in fact Mearls (who may not always remember the RAW, but clearly knows the RAI) have previously always said there is a minimum of +1 HP when levelling up.
Not that this will have any real implications on anyone's game, considering that few players ever play a low-Con PC, and if they do they will probably now ask the DM for permission to gain average HP at level-up instead of rolling.