Once you have unlocked all the playable characters and reached 25 moons you are faced with Winter and the threat of the White Walkers, an ancient race of ice creatures from the the Far North of Wasteros. Tap on the ravens to see clues on how to survive with each ruler and then play each of them again to unlock a effect personal to that particular character which will help them unlock their ending. The order in which you unlock the different rulers endings does not matter.
Below are the raven clues for each of the rulers, the effect you need to unlock for each of them and a step by step video guide showing you how it is done.
Raven clue: 'The raven stands on a burning road. The deep echo of two dragons' screams vibrates through the flames'. Daenarys unique skillset is Dragon Riders effect.
Raven clue: 'A raven flies over a large frozen lake, which exudes a green haze'. Tyrion's unique skillset is The Trap effect.
Raven clue: 'The raven pecks at the pommel of a shiny sword as scores upon scores of soldiers run smiling to their deaths'. Jaime's unique skillset is The Sword (Lightbringer) effect.
Raven clue: 'The raven is on the branch of a lonely tree, amongst a crowd of soldiers from all the Seven Kingdoms'. Sansa's unique skillset is One Kingdom effect.
Raven clue: 'The raven flies away as a failed Maester grabs a handful of glittering dust'. Jon's unique skillset is Valyrian Dust effect.
Raven clue: 'A raven flies over a red tree under which a blonde Queen strikes an unlikely alliance'. Arya's unique skillset is The Pact effect.
Raven clue: 'The raven shrieks as metallic giants emerge from the earth in front of a stag and a hidden wolf'. Gendry's unique skillset is the Horn of Winter effect.
Middle raven clue: 'A raven gazes at its reflection in a shard of dragonglass'.
As there is no ruler in the center where this raven presides, you can use any of the eight rulers to complete this task which is to make Dragonglass so you can use it against the White Walkers.