characteristics of dualscreening:
#1 - playing a map on osu!taiko, we'll call this A
#2 - syncing up something with significant changes in reading, but requiring identical keypresses, we'll call this B
#3 - watching B while playing A, using the skill required for B to submit a score for A

examples of dualscreening from the above definitions:
#1 - using a recorded video of map with nomod (B) to submit a score with FL (A)
#2 - using a second game client offline on a second computer to do #1
#3 - using a program to convert taiko keypresses into a mania map, then watching a video of the mania map (B) to submit a taiko score (A)
#4 - using a skin that changes the visual effects of taiko into mania, reading the map as if it was mania (B) to submit a taiko score (A)
#5 - using a skin that changes the visual effects of FL, you can read it as if it's nomod/HD (B) and submit a normal FL score (A)
#6 - using some resolution exploits to make HDHR or FL easier, reading the now easier mods (B) to submit a normal score (A)