Father Mateo Elder Sign (lvl 0)

Upgrades are wild:
Because of Arcane Research and Down the Rabbit Hole, you want to upgrade carefully and the "level 0" version looks a little weird:
Each Arcane Research reduces the cost of the first Spell you upgrade by 1, for a combined discount of 2xp.
Down the Rabbit Hole Discounts the first 2Cards you upgrade by 1.

This means that Upgrading Olive McBride from level 0 to level 2 costs you 1 xp if you do it first, and the Down the Rabbit Hole discount is applied.

If you were to update a spell like Ward of Protection first, you would get -1 from Down the Rabbit Hole, -1 from Arcane Research, and -1 from Arcane Research again. Meaning the total discount would be -3, more than you need for that upgrade to Ward of Protection, wasting one of the discounts.

For this reason, it's very important to be mindful of the upgrade order you apply. Generally, you want to upgrade a spell first if the upgrade costs 3 or more xp. Like Divination, Brand of Cthugha, or Blur.

You want to upgrade non spell cards like Olive McBride first if you have a spell like Ward of Protection to upgrade that does not need the full 3xp discount.

Adding new level 1 cards like Blur will cost you an extra xp, but you will get that back quickly when you upgrade them to their level 4 counterparts.

Upgrade Path:
Scenario 1
Olive McBrideOlive McBride : Costs 1xp (Down the Rabbit Hole)
Some 3xp upgrade: DivinationDivination : 0xp (-1 from Down the Rabbit Hole, -2 from Arcane Researchx2) We've got one more use from each Arcane Research to spend, so let's upgrade Ward of ProtectionWard of Protection for free : 0xp (-2 from Arcane Research) So we've upgraded a lot and only spent 1xp. If you have 2 or more xp left over, go ahead and turn Eye of Chaosany of the Divination cycle, to get the extra xp cost out of the way. We're gonna want to have that done so we can get max value out of upgrading those later.

Non-Spell Upgradables:

Spell Upgrades:

Fully Upgraded Deck: linkgoeshere