Whenever a player takes an extra turn, that player discards their hand and exiles their graveyard.
-Stranglehold is a nice start, but Magic can probably afford to have more Time Walk hate than it does. Let's face it, most people aren't taking extra turns for value, they do it because they have some way to go infinite.
Target player discards a card at random. That player can't cast spells this turn.
-I like Silence but I always felt that conceptually, it didn't make a lot of sense in white. You're forbidding me from casting spells? Why the hell should I listen to you. Now a magically induced migraine headache? That makes more sense to me.
Choose one - Target player loses 3 life, or target creature gets -0/-3.
-black bolt, but at sorcery speed. we can't have another color getting better burn than red now, can we?
Ravages of Time
Take an extra turn after this one. You lose half your staring life total, rounded up.
-Not much to say here, other than I thought it would be an interesting design. I just need to figure out what downside is most appropriate. Half current life? Half total life? 10 life? It needs to be something dramatic enough to justify the effect being bled.
At the beginning of each end step, if a player has 13 life, that player loses the game
-The natural progression of Innistrad's "13 is bad luck" theme.