Saheeli's Directive

Improvise (Each artifact you tap after you're done activating mana abilities pays for {1}.)
Reveal the top X cards of your library. You may put any number of artifact cards with mana value X or less from among them onto the battlefield. Then put all cards revealed this way that weren't put onto the battlefield into your graveyard.

Treasure Chest

Commander 2018

Improvise (Each artifact you tap after you're done activating mana abilities pays for {1}.)
Reveal the top X cards of your library. You may put any number of artifact cards with converted mana cost X or less from among them onto the battlefield. Then put all cards revealed this way that weren't put onto the battlefield into your graveyard.

All of the artifacts put onto the battlefield this way enter at the same time. If any have triggered abilities that trigger on something else entering the battlefield, they'll see each other.

Equipment attached to a creature doesn't become tapped when that creature becomes tapped, and tapping that Equipment doesn't cause the creature to become tapped.

If a card in your library has {X} in its mana cost, X is considered to be 0.

If an artifact you control has a mana ability with {T} in the cost, activating that ability while casting a spell with improvise will result in the artifact being tapped when you pay the spell's costs. You won't be able to tap it again for improvise. Similarly, if you sacrifice an artifact to activate a mana ability while casting a spell with improvise, that artifact won't be on the battlefield when you pay the spell's costs, so you won't be able to tap it for improvise.

Improvise can't be used to pay for anything other than the cost of casting the spell. For example, it can't be used during the resolution of an ability that says "Counter target spell unless its controller pays {3}."

Improvise can't pay for {W}, {U}, {B}, {R}, {G}, or {C} mana symbols in a spell's total cost.

Improvise doesn't change a spell's mana cost or mana value.

Saheeli's Directive considers the individual mana values of the artifact cards you reveal. The sum of their mana values may be greater than X.

Tapping an artifact won't cause its abilities to stop applying unless those abilities say so.

When calculating a spell's total cost, include any alternative costs, additional costs, or anything else that increases or reduces the cost to cast the spell. Improvise applies after the total cost is calculated.

When using improvise to cast a spell with {X} in its mana cost, first choose the value for X. That choice, plus any cost increases or decreases, will determine the spell's total cost. Then you can tap artifacts you control to help pay that cost. For example, if you cast Saheeli's Directive and choose X to be 3, the total cost is {3}{R}{R}{R}. If you tap two artifacts, you'll have to pay {1}{R}{R}{R}.