Though they had never left the Core, the Oltec knew the stars.

Eye of Ojer Taq // Apex Observatory

Apex Observatory enters tapped. As it enters, choose a card type shared among two exiled cards used to craft it.
{T}: The next spell you cast this turn of the chosen type can be cast without paying its mana cost.

{T}: Add one mana of any color.
Craft with two that share a card type {6} ({6}, Exile this artifact, Exile the two from among other permanents you control and/or cards from your graveyard: Return this card transformed under its owner's control. Craft only as a sorcery.)

The Lost Caverns of Ixalan Commander

Card types that may appear in a normal game of Magic are artifact, battle, creature, enchantment, instant, land, planeswalker, sorcery, and tribal (a card type found on some older cards). Supertypes such as snow and basic may not be chosen. Subtypes such as Bird, Equipment, and Forest also may not be chosen. Land may be chosen, but it's not a good idea.

Craft abilities are activated abilities with costs that have a mana component as well as an additional "materials" component.

Craft abilities are written "Craft with [materials] [mana]", which means "[Mana], Exile this permanent, Exile [materials] from among permanents you control and/or cards in your graveyard: Return this card to the battlefield transformed under its owner's control. Activate only as a sorcery."

If a card that isn't a transforming double-faced card becomes a copy of a card with craft, it'll stay in exile if you activate the craft ability. It won't return to the battlefield.

If the materials required include multiple objects, you may exile some of them from among permanents you control and the rest from among cards in your graveyard. You don't have to choose all permanents or all cards from your graveyard.

The back faces of some cards with craft refer to cards "used to craft" it. This refers to the cards exiled as part of the cost of the craft ability of the front face. Those cards are considered to be "used to craft" that permanent as long as they remain exiled and the permanent remains on the battlefield, even if the permanent's controller changes or some of its characteristics change (because of a copy effect, for example.)

You may exile tokens you control as part of the materials required. However, because they aren't cards and won't stay in exile, any abilities that refer to what you "used to craft" the back faces won't refer to anything.