This is one of my favorite intervals I put in towards the end. Using the song, Let the Bodies Hit the Floor, by Disturbed.
Seated with moderate resistance level
8 jumps, follow song, they count to 8, after the eight count, have them increase resistance to slightly heavier level, do an all out hill sprint for about 10 seconds!
Sit back, decrease resistance back to moderate, until they come back to 8 counts again, & repeat, hill attacks will get a little longer with each one. You'll have about 4 total, last one being about 20 seconds long.
I tend to repeat some of the words in the song, like, "this is not the end!" "something's got to give" "Nothing's wrong with me"
This interval will push you towards the top of the perceived exertion scale 8-9, or 85-90% MHR.