With the addition of 
Ascendant Voidcore, players can earn two weeks’ worth of 
Myth Dawncrest by using Ascendant Voidcores in Hero Track Items.
Here’s how it works:
- Obtain a Hero track Weapon or Trinket and upgrade it to 6/6 (276).
- Apply your Ascendant Voidcore to the Item, upgrading it from 276 to 285.
- That slot is now free to upgrade to Myth 5/6 (ilvl 285), saving you 60 crests for that slot.
- This can be done for both Weapon slots and Trinket slots.
That happens because the item level upgrade provided by Ascendant Voidcores is counting towards the max item level equipped per slot. It is the same reason upgrading Myth track items to 2/6 Myth doesn’t cost any crests if you already had a 6/6 Hero Track item in that slot before.
Caveats
Note that there are some caveats! The 240 crests figure comes from the crests saved when upgrading 2 trinkets and 2 weapons (4 x 60 = 240). If you have already spent Myth crests on Weapons or Trinkets (including crafting), or if you use a two-handed weapon, you will save fewer crests. If both your trinkets and both your weapons are already at or above 285, you can’t save crests with Ascendant Voidcores.
Remember that both Trinkets and Weapons have peculiarities when doing item upgrades. For instance, you will only save crests with trinkets after upgrading two items to a given item level. Weapons can be annoying when swapping from dual-wielding to two-handed weapons, or vice versa.
Step by Step in Practice
Below is a practical example of the crest saving method. You can see at the start that the macro displays that Trinkets are free to be upgraded up to 276 (6/6 Hero or 2/6 Myth). Then, I upgrade my 6/6 Hero 
Gaze of the Alnseer using the Ascendant Voidcore. Running the same macro again, it now shows that I can upgrade trinkets up to 285 without spending crests.
You can check the results yourself by using the macro below:
/run x={}for n,i in next,Enum.ItemRedundancySlot do w=C_ItemUpgrade.GetHighWatermarkForSlot(i)x[i]={w>677,w,n}end for i,v in next,x do if i<12 and not v[1]or i>11 and not(x[12][1]or x[13][1]and x[16][1]or x[14][1]and x[15][1])then print(v[2],v[3])end end Farming Ascendant Voidcores
With the recent hotfix, you can farm Voidcores quickly from Mythic+ and Raids, with guaranteed 
Ascendant Voidshard drops from +10 or higher keys or Heroic/Mythic raid bosses. Your first two Nightmare Preys of the week also have guaranteed Voidshards inside their reward chest.
