This blue-red deck is much more aggressive than other Delver decks you may see. It gets the most use out of prowess and looks to cast many spells in one turn. Gitaxian Probe, Vapor Snag, Lightning Bolt, and Serum Visions are great at accomplishing this. There's also plenty of countermagic that's useful for disrupting our opponent or protecting our creatures.

And if you have a few lying around, Abbot of Keral Keep from Magic Origins can be a great addition to this deck as well. Since it's a rare from a recent set, it's a bit easier to find.

Tips on Playing the Deck:

It's usually a mistake to keep a hand without at least one creature. Regardless of how good the hand looks, it's crucial to drop a creature early. While it may look like you're doing well in Remanding and Mana Leaking everything, this deck does not want to prolong the game. It wants to win as quickly as possible.
Gitaxian Probe is our most useful spell. It's great that it triggers our prowess, but it's also really good for knowing how to play against your opponent. If you know their hand, you'll know if you should use your Mana Leak now or if you should save it for something more threatening later.
Save Serum Visions until after you've played Delver of Secrets, or until there is something specific you need. Serum Visions is a fun card to play, and it's really tempting to cast on turn one. Who doesn't love scrying? However, in this deck you may need specific answers at specific times. If you cast Serum Visions on turn one on the play and see a Vapor Snag and a Lightning Bolt, how will you know if you should keep them? They are awful cards against decks like Tron, Storm, or any creature-light deck, but are amazing against Affinity or Zoo. Waiting to cast Serum Visions until you know what your opponent is playing is almost always a better play, and it's good at helping you transform your Delver, too.
How to Fight Eldrazi:

Vapor Snag really shines against Eldrazi. Bouncing their large monsters can buy you enough time to get some damage through. The loss of 1 life really helps, too.
Electrolyze is great against Eldrazi Mimic, Eldrazi Skyspawner, and Eldrazi Scion tokens.
The creatures in this deck are great at getting past Eldrazi. Insectile Aberration and Stormchaser Mage are hard to block, and Young Pyromancer can create enough tokens to overwhelm them.
Lastly, the super-secret sideboard tech for beating Eldrazi is Spreading Seas. Spreading Seas on Eye of Ugin or Eldrazi Temple really slows down the Eldrazi deck, and you get to draw a card as well!