Dekver of Secrets

[JBlaze]

What are the rules regarding Delver of Secrets upkeep trigger? Am I allowed to cast a brainstorm or crack a fetch after I look at the top card of my library but before I reveal to my opponent?

[Koby]

What are the rules regarding Delver of Secrets upkeep trigger? Am I allowed to cast a brainstorm or crack a fetch after I look at the top card of my library but before I reveal to my opponent?

Delver of Secrets has exactly one trigger. When it resolves, you look at the card and may reveal it. If it meets the condition, Delver of Secrets will transform.

No player has priority during these actions. Looking at the top card and revealing it are tied into one ability and must be performed at the same time.

[Justin]

Delver of Secrets has exactly one trigger. When it resolves, you look at the card and may reveal it. If it meets the condition, Delver of Secrets will transform.

No player has priority during these actions. Looking at the top card and revealing it are tied into one ability and must be performed at the same time.

Correct. You may brainstorm with the trigger on the stack to make sure that your Delver transforms. Once you look at the card, you may crack a fetch land if you prefer a random card to the one you peeked at. However, you may not peak at or reveal the top card after cracking the fetchland. Delver has only one trigger.

[John Cox]

Just for clarification could you do this at the beginning of your upkeep before the trigger goes on the stack to use two brainstorms and crack a fetchland?

[Tempus]

There's no before the trigger goes on the stack.
The first thing in upkeep is, that Delver's trigger goes on the stack.

However, you can respond to an item on the stack as much as you want to. So in response to the trigger you can Brainstorm, the fetch, then Brainstorm again