@JeremyECrawford Can a creature with multiple speeds choose which one to use to stand up from prone? e.g. Can a creature with 0 walking speed, or higher walking speed than flying speed, choose to stand using their flying speed?
— Armando Doval (@armando_doval) February 4, 2018
The rule on standing up from prone fails to account for you having multiple speeds. Here's the intent: if you have multiple speeds and stand up, expend an amount of movement equal to half your highest speed. #DnD https://t.co/bIsUZRdk0W
— Jeremy Crawford (@JeremyECrawford) February 4, 2018
That ruling still leaves room for gaming the system if you have a speed that is five to ten feet higher than another somehow. Spend half your walking movement (35 ft) and still have 30 ft of flight movement. I would just halve all speeds for getting up from prone. That scenario is covered by the rule on using multiple speeds.
— Jeremy Crawford (@JeremyECrawford) February 4, 2018