Phyrexian Dragon Engine — ruling 1

When a pair of cards are melded, the result is a single creature that's represented by two cards. If the melded creature dies, both cards are put into your graveyard. As it leaves the battlefield, both of those cards are turned face up again. If the cards are put on the top or bottom of your library, you choose their relative order.

Phyrexian Dragon Engine — ruling 2

One card in each pair of meld cards has an ability that instructs you to exile the two cards and meld them. If you control more than one object with one of those names, you select one object with that name to exile.

Phyrexian Dragon Engine — ruling 3

When two cards are exiled and melded, they each leave the battlefield, then return together as one new object with no relation to either of the objects that left the battlefield. Counters, Auras, Equipment, and other effects that affected those two cards don't affect the melded permanent.

Phyrexian Dragon Engine — ruling 4

Only two cards belonging to the same meld pair can be melded. Tokens, cards that aren't meld cards, or meld cards that don't form a meld pair can't be melded. If an effect instructs a player to meld cards that can't be melded, those cards remain in exile.

Phyrexian Dragon Engine — ruling 5

While a meld card is in any zone other than the battlefield, it has only the characteristics of its front face. The same is true while it's on the battlefield with its front face up.

Phyrexian Dragon Engine — ruling 6

While a melded permanent is on the battlefield, it has only the characteristics of its combined back face. Any effects that modify how the new object enters the battlefield will consider only the combined back face.

Phyrexian Dragon Engine — ruling 7

Note that the permanent represented by the combined back faces has a color indicator.

Phyrexian Dragon Engine — ruling 8

The mana value of a melded permanent is the sum of the mana values of its front faces. A creature that becomes a copy of a melded permanent has only the characteristics of that combined back face, and its mana value is 0.

Phyrexian Dragon Engine : règles, fonctionnement et interactions (MTG)

Phyrexian Dragon Engine is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Double strike When this creature enters from your graveyard, you may discard your hand. If you do, draw three cards. Unearth (Melds with Mishra, Claimed by Gix.)

How it works : Phyrexian Dragon Engine

Original English text — Wizards of the Coast / Scryfall

#1October 14, 2022· Wizards of the Coast
When a pair of cards are melded, the result is a single creature that's represented by two cards. If the melded creature dies, both cards are put into your graveyard. As it leaves the battlefield, both of those cards are turned face up again. If the cards are put on the top or bottom of your library, you choose their relative order.
No other card is named in this ruling.
#2October 14, 2022· Wizards of the Coast
One card in each pair of meld cards has an ability that instructs you to exile the two cards and meld them. If you control more than one object with one of those names, you select one object with that name to exile.
No other card is named in this ruling.
#3October 14, 2022· Wizards of the Coast
When two cards are exiled and melded, they each leave the battlefield, then return together as one new object with no relation to either of the objects that left the battlefield. Counters, Auras, Equipment, and other effects that affected those two cards don't affect the melded permanent.
No other card is named in this ruling.
#4October 14, 2022· Wizards of the Coast
Only two cards belonging to the same meld pair can be melded. Tokens, cards that aren't meld cards, or meld cards that don't form a meld pair can't be melded. If an effect instructs a player to meld cards that can't be melded, those cards remain in exile.
No other card is named in this ruling.
#5October 14, 2022· Wizards of the Coast
While a meld card is in any zone other than the battlefield, it has only the characteristics of its front face. The same is true while it's on the battlefield with its front face up.
No other card is named in this ruling.
#6October 14, 2022· Wizards of the Coast
While a melded permanent is on the battlefield, it has only the characteristics of its combined back face. Any effects that modify how the new object enters the battlefield will consider only the combined back face.
No other card is named in this ruling.
#7October 14, 2022· Wizards of the Coast
Note that the permanent represented by the combined back faces has a color indicator.
No other card is named in this ruling.
#8October 14, 2022· Wizards of the Coast
The mana value of a melded permanent is the sum of the mana values of its front faces. A creature that becomes a copy of a melded permanent has only the characteristics of that combined back face, and its mana value is 0.
No other card is named in this ruling.
#9October 14, 2022· Wizards of the Coast
A player prompted to name a card may name the combined back face, and each player has the right to know that combined back face's characteristics at all times.
No other card is named in this ruling.
#10October 14, 2022· Wizards of the Coast
If an effect moves a melded permanent to a new zone and then affects "that card," it affects both cards.
No other card is named in this ruling.
#11October 14, 2022· Wizards of the Coast
In the Commander variant, a meld card's color identity is determined only by the mana costs and mana symbols in the rules text of its front face. No symbols or rules text of the permanent it melds into are considered.
No other card is named in this ruling.
#12October 14, 2022· Wizards of the Coast
If you activate a card's unearth ability but that card is removed from your graveyard before the ability resolves, that unearth ability will do nothing as it resolves.
No other card is named in this ruling.
#13October 14, 2022· Wizards of the Coast
Activating a card's unearth ability isn't the same as casting that card. The unearth ability is put on the stack, but the card is not. Spells and abilities that interact with activated abilities (such as Defabricate's second mode) will interact with unearth, but spells and abilities that interact with spells (such as Scatter Ray) will not.
No other card is named in this ruling.
#14October 14, 2022· Wizards of the Coast
At the beginning of the next end step, a permanent returned to the battlefield with unearth is exiled. This is a delayed triggered ability, and it can be countered by effects such as Defabricate that counter triggered abilities. If the ability is countered, the permanent will stay on the battlefield and the delayed triggered ability won't trigger again. However, the replacement effect will still exile the permanent if it eventually leaves the battlefield.
No other card is named in this ruling.
#15October 14, 2022· Wizards of the Coast
Unearth grants haste to the permanent that's returned to the battlefield (even if it's not a creature card). However, neither of the "exile" abilities is granted to that permanent. If that permanent loses all its abilities, it will still be exiled at the beginning of the next end step, and if it would leave the battlefield, it is still exiled instead.
No other card is named in this ruling.
#16October 14, 2022· Wizards of the Coast
If a permanent returned to the battlefield with unearth would leave the battlefield for any reason, it's exiled instead—unless the spell or ability that's causing the permanent to leave the battlefield is actually trying to exile it! In that case, it succeeds at exiling it. If that spell or ability later returns the card to the battlefield (as Static Net might, for example), the permanent card will return to the battlefield as a new object with no relation to its previous existence. The unearth effects will no longer apply to it.
No other card is named in this ruling.
#17October 14, 2022· Wizards of the Coast
Powerstone tokens are a kind of predefined token. Each one has the artifact subtype "Powerstone" and the ability ": Add . This mana can't be spent to cast a nonartifact spell."
No other card is named in this ruling.
#18October 14, 2022· Wizards of the Coast
You can use the added by a Powerstone token on anything that isn't a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.
No other card is named in this ruling.
#19October 14, 2022· Wizards of the Coast
Although all the cards in The Brothers' War that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn't part of the token's definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won't enter the battlefield tapped.
No other card is named in this ruling.

Interactions with other cards

These cards' text mentions Phyrexian Dragon Engine.

Mishra, Claimed by Gix

Whenever you attack, each opponent loses X life and you gain X life, where X is the number of attacking creatures. If Mishra, Claimed by Gix and a creature named Phyrexian Dragon Engine are attacking, and you both own and control them, exile them, then meld them into Mishra, Lost to Phyrexia. It enters tapped and attacking.