Sower of Temptation & Phyrexian Metamorph

[A.-1.]

Sower of Temptation 
Creature — Faerie Wizard
Flying
When Sower of Temptation enters the battlefield, gain control of target creature for as long as Sower of Temptation remains on the battlefield.
P/T:
2/2

Phyrexian Metamorph 3
Artifact Creature — Shapeshifter
(Phyrexian Blue can be paid with either Blue or 2 life.)
You may have Phyrexian Metamorph enter the battlefield as a copy of any artifact or creature on the battlefield, except it's an artifact in addition to its other types.
P/T:
0 / 0

Duplicant 
Artifact Creature — Shapeshifter
Imprint — When Duplicant enters the battlefield, you may exile target nontoken creature.
As long as the exiled card is a creature card, Duplicant has that card's power, toughness, and creature types. It's still a Shapeshifter.
P/T:
2 / 4

Kuldotha Forgemaster 
Artifact Creature — Construct
, Sacrifice three artifacts: Search your library for an artifact card and put it onto the battlefield. Then shuffle your library.
P/T:
3 / 5

Player A casts Sower of Temptation targeting Player B's Duplicant.
Player B responds by activating their Kuldotha Forgemaster, sacrificing the Forgemaster and two additional creatures other than the Duplicant. Player B searches up a Phyrexian Metamorph copying Player A's Sower of Temptation. The Metamorph, now Sower, targets Player A's Sower.

After Player B's Metamorph (Sower) ability resolves, what happens to the initial Sower's trigger? Does Player A gain control of the Duplicant even though they no longer control the Sower or does Player B get to maintain control of their Duplicant?

I think this rule is the one that most applies to this scenario: 603.7d If a spell creates a delayed triggered ability, the source of that delayed triggered ability is that spell. The controller of that delayed triggered ability is the player who controlled that spell as it resolved.

This leads me to believe that Player B gets to maintain control of their Duplicant.

[bactgudz]

I assume you mean that player B responds to sower's trigger by using forgemaster, not the casting of sower...otherwise the metamorph couldn't copy sower in the first place.

There is no delayed trigger.  Sower's ETB ability is put on the stack under player A's control when sower ETB.  Thus player A gains control of the duplicant.

Now if player B had metamorphed the duplicant and then removed sower with metamorph/duplicants ability, then player B would retain control of the original duplicant.  This is because sower's ETB ability creates a continuous effect with a duration.  That duration has already expired by the time the ability resolves, so it would do nothing.

[A.-1.]

I assume you mean that player B responds to sower's trigger by using forgemaster, not the casting of sower...otherwise the metamorph couldn't copy sower in the first place.

Yes. Sorry for the confusion, and thanks for clarifying. I looked through way more of the comprehensive rules than I would ever like to again and couldn't find exactly what I needed to answer my own question.

Are there any common examples of delayed triggers in Vintage? Necropotence?

[bactgudz]

I assume you mean that player B responds to sower's trigger by using forgemaster, not the casting of sower...otherwise the metamorph couldn't copy sower in the first place.

Yes. Sorry for the confusion, and thanks for clarifying. I looked through way more of the comprehensive rules than I would ever like to again and couldn't find exactly what I needed to answer my own question.

Are there any common examples of delayed triggers in Vintage? Necropotence?

Mana Drain is a spell that creates a delayed triggered ability, so 603.7d is applicable. Necropotence's ability creates a delayed triggered ability to put the card in hand, an activated ability created it so 603.7e is applicable.