Weaponized Scrap — ruling 1

The card with upgrade moves to the battlefield, but it doesn’t enter the battlefield. Instead it overlays an artifact you control. That artifact becomes represented by the new card – if it was tapped, it’s still tapped; if it had counters on it, it still has those counters; if it was attacking, it’s still attacking; and so on.

Weaponized Scrap — ruling 2

Enters-the-battlefield triggers won’t trigger when an artifact with upgrade overlays another artifact.

Weaponized Scrap — ruling 3

If you can’t choose an artifact you control while applying a permanent’s upgrade replacement effect, it doesn’t move to or enter the battlefield at all and instead moves to exile.

Weaponized Scrap — ruling 4

An artifact can be upgraded more than once.

Weaponized Scrap — ruling 5

If the upgraded object moves to the top or bottom of its owner’s library, that player chooses the relative order for its component cards without revealing that order.

Weaponized Scrap — ruling 6

If a player’s commander is upgraded, the resulting creature is still their commander. If it leaves the battlefield, the commander can be put into the command zone instead, and the other cards move to the expected zone.

Weaponized Scrap : règles, fonctionnement et interactions (MTG)

Weaponized Scrap 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

Upgrade (This creature enters covering another artifact you control. If it can't, exile it. Ignore the artifact it's covering. Anywhere this card goes, cards underneath it also go. It has haste.)

How it works : Weaponized Scrap

Original English text — Wizards of the Coast / Scryfall

#1November 12, 2019· Wizards of the Coast
The card with upgrade moves to the battlefield, but it doesn’t enter the battlefield. Instead it overlays an artifact you control. That artifact becomes represented by the new card – if it was tapped, it’s still tapped; if it had counters on it, it still has those counters; if it was attacking, it’s still attacking; and so on.
No other card is named in this ruling.
#2November 12, 2019· Wizards of the Coast
Enters-the-battlefield triggers won’t trigger when an artifact with upgrade overlays another artifact.
No other card is named in this ruling.
#3November 12, 2019· Wizards of the Coast
If you can’t choose an artifact you control while applying a permanent’s upgrade replacement effect, it doesn’t move to or enter the battlefield at all and instead moves to exile.
No other card is named in this ruling.
#4November 12, 2019· Wizards of the Coast
An artifact can be upgraded more than once.
No other card is named in this ruling.
#5November 12, 2019· Wizards of the Coast
If the upgraded object moves to the top or bottom of its owner’s library, that player chooses the relative order for its component cards without revealing that order.
No other card is named in this ruling.
#6November 12, 2019· Wizards of the Coast
If a player’s commander is upgraded, the resulting creature is still their commander. If it leaves the battlefield, the commander can be put into the command zone instead, and the other cards move to the expected zone.
No other card is named in this ruling.