The guillotine in my opinion is the most versatile submission in all of grappling

The guillotine in my opinion is the most versatile submission in all of grappling. This choke can be used offensively standing as @briantcity showed, but also defensively to counter a takedown, used in the guard, while on top, to pass and to finish a takedown. All that is needed is wrapping your arm around the neck.
.
Most submission holds first require positional control on the ground prior to initiating the submission, however with the ease of application this technique breaks this rule.