In this last case the win condition presented by Thassa's Oracle wont work
Grixis Dragons - Magic 2019 Standard | ASTRALPLANE, (5-0) MTGO Creatures (20) 2 Demanding Dragon 2 Pia Nalaar 4 Glorybringer 4 Goblin Chainwhirler 4 Nicol Bolas, the Ravager 4 Scrapheap Scrounger Planeswalkers (5) 2 Sarkhan, Fireblood 3 Chandra, Torch of Defiance Instants (8) 2 Magma Spray 2 Unlicensed Disintegration 4 Abrade Artifacts (2) 2 Heart of Kiran Lands (25) 6 Mountain 1 Scavenger Grounds 2 Aether Hub 4 Canyon Slough 4 Dragonskull Summit 4 Spirebluff Canal 4 Sulfur Falls Sideboard (15) 1 Angrath, the Flame-Chained 1 Magma Spray 1 Hour of Glory 1 Spit Flame 2 Chandra's Defeat 3 Negate 1 Banefire 2 Doomfall 3 Duress When Sarkhan, Fireblood and Chandra, Torch of Defiance come together in the same deck, you have the possibility of some explosive turns
You can give it to your opponents and goad it to start chaos amongst your enemies
In other words, how valuable is scry
It's reactive and proactive, it kills and sets up draws, and it works beautifully in a Zombie deck, although it doesn't require it