They do this via counter attack or revenge. 

Basically, they will use a champion with strong a1, gear it very slow so enemy will move first. If the champion manage to counter attack every turn and 1 hit every enemy then no turn will be recorded. 

If rng is involve, they will try and try again until they get the lowest possible turn. 

The title of the post has been changed to better reflect the question you asked.

Please use clear titles that allow other users to understand what you are going to ask. This way you can attract a good answer faster.

Desolé traducteur  français / anglais

when i saw that was sneaky counter attackers in super slow speeds - well played