Surrender?

[OKIJIN]

 

This card can only be activated if you have 4 or more monsters on the field and 4 magic or trap cards on the field. When activated your opponent must do one of the following effects.

Effect 1: Banish all cards on their side of the field, in their hand, and the top 5 cards of their deck and graveyard.

Effect 2: Lose half of their life points.

[Trebuchet MS]

This card can only be activated If you have control 4 or more monsters on the field and 4 magic or other Spell/Trap cards: on the field. When activated Your opponent must do chooses one of these following effects.

Effect 1: * Banish all cards you control on their side of the field, in their your hand, in your Graveyard, and the top 5 cards of their your Deck and graveyard.

Effect 2: * Lose half of their Halve your Life Points.

Essentially, a winmoar card. For effects that force your opponent to do something, like Dark Coffin and Changing Destiny, take note that the effect applies from their point of view.

 

That said, the opponent is very, very likely to simply halve their own Life Points every time, especially late in the game where the Life Point count can get incredibly small. Also, since you already need an impressive field presence to activate this card, the opponent will want to keep their setup because if they don't, they become unable to respond to your field presence, and the game would just end right there.

 

To remove this illusion of choice, I'd split the first effect into 2 parts (e.g. banish all monsters or banish all S/Ts) and leave the opponent to decide between that, so that you at least get something more tangible out of the opponent's decision.