If Diana pulls in one or more enemy champions, the moonlight crashes down onto her after one second, dealing 200/300/400 (+0.6 ability power) magic damage in an area around her, increased by 35/60/85 (+0.15 ability power) for each target beyond the first pulled
Diana's old ultimate, Lunar Rush, is now her new E. The cooldown is 22/20/18/16/14, as opposed to 25/20/15. The cost is 40/45/55/60/65 as opposed to 50/65/80 mana. The damage is 40/60/80/100/120 instead of 100/160/220.
basically, diana trades off about 60-100 less damage for her dash and gains 200-400 extra damage she gains with her ultimate, which scales, and does AoE damage that can blow up their entire team.
It's simple math buddy.