I am an anime only for Bang Dream so my review will be based on only what I know from the anime. This two episode special introduces Morfonica a new band to the audience. It a violin rock band with 5 members. The story mainly focus on the lead singer Mashiro and her childlike imagination and her past. The art for this is beautiful. The water colour looking animation for Mashiro's imagination is just beautifully animated and really some of the best in the whole series so far. The animation is really good to it has some flaws which come with full CGI anime but inno way is it bad CGI. It can look really good at times.
The ost is also really good and fits perfectly with the scenes. As for the music it is banger like always.
I highly recommend this anime to people who have watched the series till now and also new people as it has no relation to the series before as far as plot goes.
My score for this special is: 9/10