If I discard Anje's Ravager on an opponents turn, can I cast it for the madness cost at that time? Or do I have to wait until it's my turn to discard and cast it?
To be clear, you choose to cast Anje's Ravager this way when the madness triggered ability resolves — and not later (C.R. 702.34a). Anje's Ravager is cast this way at a moment that spells normally can't be cast (not even instant spells) (C.R. 608.2f). See also this thread.
...do I have to wait until it's my turn to discard and cast it?
Just making sure...
If an opponent's card tells you to discard a card, you can't wait: you have to do it right away.
Furthermore, having Madness printed on a card does not allow a player to discard such card at will.
You can't simply choose to discard Anje's Ravager; you NEED some external way to discard it.
If an opponent's card tells you to discard a card, you can't wait: you have to do it right away.
Furthermore, having Madness printed on a card does not allow a player to discard such card at will.
You can't simply choose to discard Anje's Ravager; you NEED some external way to discard it.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules