Continuity mistake: Mima is watching Rumi set up her new computer. In the reflection of the monitor, we can see a calendar on the wall behind him. The first number on the bottom row of calendar is 26 in the reflection. A minute later, when Rumi asks "what are you going to do with a clip", we can see the calendar in the background and it is now the number 27 shown to be the first number on the bottom row. The number 27 also changes colour from black to red in between the two shots. (00:19:02 - 00:20:12)
Revealing mistake: When Jack is melting after being showered with acid, at one point, there's a very obvious cross-dissolve used to blend two shots into one as Jack is reduced into a skeleton. It almost works, except suddenly, the snow around him is slightly different. (Some impressions into the snow and whatnot appear during the fade that shouldn't, as does a few pieces of debris.)