Hot answers tagged magic-the-gathering
Hexproof only prevents targeting. Any effects that affect the player without targeting (e.g. "Deal 2 damage to each opponent") still work. Draconic Roar doesn't target your opponent, so his hexproof has no effect.
While both answers answer the specific case, would like to explain a bit more broadly, since the question is a lot more broadly worded than the specific instance. Since the player has hexproof, but the card Draconic Roar does not say 'target player', all effects of the spell will occur. However, a very similar card, Searing Blaze instead reads: Searing ...
Hexproof is very simple: if a spell or ability uses the word "target", that target can't legally be that player. It doesn't affect damage, or life loss, or anything else once the spell is resolving. In the specific case of Draconic Roar, the only target you choose is a creature, so it is legal to cast and it resolves. The Leyline can't affect what happens ...
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