Final Chapter
Enchantment (R)
When this enchantment enters the battlefield, you cannot declare attacks until end of turn.
No more than one creature can attack or block each combat.
Whenever a creature attacks, it gains Trample and "Players dealt combat damage by this creature lose the game" until end of turn.

I think the trample and single combat part is a really cool idea. I feel ending the game outright could be anti-climactic, though, and probably the simplest way to use this is to just use an evasive creature.

This is a different idea, but what do you think of something like this?

Nearly Final Chapter 2RW
Enchantment
No more than one creature can attack or block each combat.
All creatures have trample.
If a creature would deal combat damage to a player, it deals twice that much damage instead.