River of Souls (Rift Event)  

ok, so i got the shard 1st on Faemist for the Shadetouched Weapons Cache... what it gave me was a selection (for a warrior) of either a Barghest Bone Blade (DPS: 21.7, 32-59 damage every 2.1 sec, strength+5, Endurance+14, Parry+12, Hit+8), or a Dragonbone pike (from memory). I chose the Barghest, so i cant give specifics on the other, but it is a spear and a 2 hander (obviously)

The quest objectives are to obtain 5 shadetouched scepters from invasions, 3 shadetouched blades from rifts, and 1 more shadetouched piece of gear from a colossus (zone invasion boss, harbinger of alsbeth)

These have to be from experience-giving invasions/rifts/zone-events

any more information that i have missed would be appreciated

Useful guide, not so helpful as regards the achievements.

Listed under 'Legacy'
Grim Bounty - collect 300 Otherworldly Sourcestone; 40 per day from daily quests plus extra from closing death rifts, defeating death invasions/footholds (quantity received based, afaik, on relative levels as well as contribution).

Grim Survivor - identify the origin of Evanescing Shadestone; quest item rewarded as part of the loot from closing a death rift (may need to be one that is part of the event and/or one that is no more than 7 levels lower than your own level), complete the quest to get the achievement.

Grim Hero - participate in the Grim Harvest final event; presumably requires participation in the final phase of the event.

Grim Protector - participate in the Grim Harvest zone invasions; I originally thought this referred to zone invasions in phase 1, but unless there is also an unstated requirement that you must take part in an invasion no more than 7 levels lower than your own level, it may be referring to the collossi invasions of phase 2 (this would make sense, as there is then one achievement specific to each phase).

Grim Victory - unlock all Grim Harvest achievements; get all the other four achievements.

Where do you get a Corrupted Essence? Everything else was clearly laid out.

I got the breadcrumb quest in Sarlet Gorge. I suspect they are in every major hub, and disappear once you accept the first one (similar to the soul quests in the capital cities).