The leak also briefly mention that certain characters can transform mid battle. (kofworld.com)
Yeah it seems like the footage started mid battle, after attack had already been chosen. (neogaf.com)
There are some smart improvements on this game compared to Hyrule Warriors, such as being able to switch characters mid battle and give commands to those you aren't controlling, but, overall I feel Hyrule Warriors is the superior game. (metacritic.com)