Riddlekeeper

[EvoLveR]

Does this mean...lets say opponent attacks with 2 creatures...does that person mill 4 cards due to  {Riddlekeeper} effect?

[TheRagingMage]

Does this mean...lets say opponent attacks with 2 creatures...does that person mill 4 cards due to  {Riddlekeeper} effect?

Yes.  Let me find a rule that says why.

[TheRagingMage]

118.9.: Some triggered abilities are written, "Whenever [a player] gains life, . . . ." Such abilities are treated as though they are written, "Whenever a source causes [a player] to gain life, . . . ." If a player gains 0 life, no life gain event has occurred, and these abilities won't trigger.
Example: A player controls Ajani's Pridemate, which reads "Whenever you gain life, you may put a +1/+1 counter on Ajani's Pridemate," and two creatures with lifelink. The creatures with lifelink deal combat damage simultaneously. Ajani's Pridemate's ability triggers twice.

[TheRagingMage]

603.2c: An ability triggers only once each time its trigger event occurs. However, it can trigger repeatedly if one event contains multiple occurrences. See also rule 509.4.
Example: A permanent has an ability whose trigger condition reads, "Whenever a land is put into a graveyard from the battlefield, . . . ." If someone casts a spell that destroys all lands, the ability will trigger once for each land put into the graveyard during the spell's resolution.