Memento of the Dalish is an Act 3 companion quest for Merrill in Dragon Age II.
Obtain Sylvanwood Ring from the Thief Leader near the entrance of Sundermount in Act 3. You can get a second one in a corpse at the assassin's lair during A Murder of Crows.
Visit Merrill's Home at the Kirkwall Alienage in Lowtown and talk to her. If she is Hawke's romance partner, speak with her at the Hawke Estate in Hightown.
As depicted by the carvings in the ring, she tells you the story of the Betrayal, plotted by the Dread Wolf, Fen'Harel.
If she is friends with Hawke, she appreciates the keepsake. If otherwise, she claims she lost one of these, and regains another with the gift. Regardless, Merrill thanks Hawke for it.
Merrill: friendship (+15) with existing friendship or Merrill: rivalry (+15) with existing rivalry.
Sylvanwood RingSylvanwood Ring
+2% critical chance
+8% critical damage
+4% nature damage
Note: You only gain one Sylvanwood Ring, even if you loot both locations.