I made a thread about this earlier, but was told I should post here instead. In this
video, when showing off Mega Metagross's speed, it outsped Sceptile. As of XY, turn order is determined before mega evolution activates. They were both lv 100 in this clip, meaning that unless if both their natures and EVs were rigged (Metagross Jolly 252 Speed EVs, Sceptile Hindered Speed 0 EVs), the Sceptile should have still outsped.
Could the rules governing mega evolution have changed? Or is it more likely that Pokemon Get☆ TV had just tinkered with the stats (or Trick Room/Sticky Web), such that they could skip straight-away to showing off Mega Metagross?