It takes half a bar, it seems to be more powerful and accurate than the normal attacks, that’s what this lady sez. And it’s great for pkin, cuz it makes you unable to run! Thanks for joeluck for this info.
EDIT: I just checked RS’s manual. here’s a quote:
Dragon Scimitar - Sever
This attack is more accurate and, if successful, will prevent your opponent from running for 10 seconds.
Comments are welcome!