Goku: Bringing my family into this is a dirty move, Eis!
Eis Shenron: But dirty moves work better than clean ones, and I'll do
anything to win this!
~ Super Saiyan 4 Goku berating Eis Shenron for using granddaughter as a shield..

The very opposite of an Honorable Villain, these villains resort to cheating to win. As most conflicts in fiction are matters of life and death/Good vs. Evil and thus have no actual "rules," most characters in this category come from stories involving some sort of contest.

Cheaters can also be involved as in infidelity.