This is a combo I've taught in all levels, to all ages. Its easy enough for the entry level class but can be made more intense by getting lower, using the legs or the leg alternative makes it more interesting for a kickboxing format.
Kickboxing alternate:
Replace squat/knee/squat/kick with:
Squat, front kick right, side kick left, right back kick, left back kick, repeat 2-4 times
How to build it:
Start in right guard (right leg toward mirror, left back, wide stance)
Jab to mirror, duck back (squat back on left) 8x
Hook to mirror, duck back 8x
Upper to mirror, duck back 8x
Cue offensive attack on punch, defensive guard on duck. Get low in the legs to burn quads, crunch abs on the duck
Combine punches:
Jab, duck, hook, duck, upper, duck 4x
Square to mirror, squat
Pick up the right knee when you come up from the squat, this should be on the top of the next measure.
From the squat, right knee, squat, left front kick
I have my class repeat the squat knee, squat kick 8x on the first round, then twice for the remainder of the combo.
Enjoy!