2017-11-17 : If a Dragon entering the battlefield causes Dragon Tempest’s second ability to trigger but leaves the battlefield before that ability resolves, that Dragon still deals damage.

2017-11-17 : The amount of damage dealt by the Dragon that entered the battlefield is based on the number of Dragons you control when the ability resolves.

2017-11-17 : The two abilities aren’t mutually exclusive. If a Dragon with flying (which is most of them) enters the battlefield under your control, both abilities will trigger.