I love this workout because it's really fast but also extremely intense. All you'll need is a weighted rope which you can normally find at your gym. 

Alternate between the three exercises below. Do each for 30 intense seconds and then rest 30 seconds. Repeat 4 times for a total of 12 minutes:

Move ropes forcefully up and down together. Arms should be narrow and you should be making big arching curves with the ropes. 

Move ropes forcefully up and down one at a time. Arches should still be as large as possible. 

Move ropes in and out together in an S motion. Arms move out and then back in, together.