Reaper of Souls - Achievement Guide - Words of Wisdom

0:00 - About Malthael - begin at Act 5.2 (Souls of the Dead); speak with Tyrael in The Sanctuary Enclave.
0:44 - The Sliver - begin at Act 5.2 (Souls of the Dead); speak with Tyrael in The Sanctuary Enclave.
1:10 - Malthael's Reapers - begin at the "Gideon's Row" quest-checkpoint under Act 5.2 (Souls of the Dead); speak with Tyrael in The Sanctuary Enclave.
1:33 - Sliver of the Stone - begin at the "Talk to the Mystic" quest-checkpoint under Act 5.2 (Souls of the Dead); speak with Tyrael in The Sanctuary Enclave.

Begin at Act 5.3 (The Harbinger). Speak with Tyrael to advance the quest, skip (or watch) the cutscene. After that, four conversations will be available:
2:00 - Urzael
2:14 - Malthael's Mercy
2:51 - Tyrael's Pain
3:13 - The Black Soulstone

3:36 - Tyrael's Mood - begin at Act 5.4 (The Witch); speak with Tyrael in The Sanctuary Enclave.
4:09 - The Angels - immediately after having the conversation "Tyrael's Mood" with Tyrael, speak with the Mystic to advance the quest. Then return to Tyrael to have the conversation "The Angels."

Begin at Act 5.7 (Breaching the Fortress). Waypoint to The Siege Outpost, and have the following conversations with Tyrael:
4:43 - About Pandemonium
5:11 - Malthael's Disappearance
5:43 - The Fortress

Following the above, board the ram, complete the event, run into the Pandemonium Fortress, and have the last conversation with Tyrael. Alternatively, exit the game, begin at Act 5.8 (Angel of Death), waypoint to the Pandemonium Fortress Level 1, and have the conversation.
6:17 - The Pandemonium Fortress