So it definitely doesn't have shards and ability scrolls for all heroes, so been trying to track which ones it does offer, so can make a strategy about what to buy. Here's what I've seen so far:

Lady of Dragonstone - Though no scrolls, maybe gone since her limited time summon is gone?

Breaker of Chains

Alvar

Jon, The Old Bear's Steward

Relina, Mysterious Wildling

Scarnest the Cruel

Brynden, Bloodraven - Scrolls only, no shards. Makes sense since you get tons of his shards via challenges

Mayla, Wood's Witch - Scrolls only, no shards. No idea what's going on here

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I thought maybe it's related to what you unlocked and I haven't unlocked all heroes, but doesn't seem to be the case since I haven't unlocked Scarnest and his shards show up often. Anything I'm missing?

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And Relina oddly her scrolls show up with Thosa's mask.. Same person?!? (It's like a Clark kent disguise, but yea probably a bug)