Activate Primal Wellspring and the two additional lands by tapping them, adding {1}{U}{U} and creating a delayed triggered ability.
Cast Frantic Search by paying {2}{U}.
Primal Wellspring's ability triggers, copying Frantic Search.
Resolve the copy of Frantic Search, looting twice and untapping Primal Wellspring and the two other lands.
Activate Primal Wellspring and those two lands, adding at least {1}{U}{U} and creating another delayed triggered ability.
Cast Narset's Reversal by paying {U}{U}, targeting Frantic Search.
Primal Wellspring's ability triggers, creating a copy of Narset's Reversal targeting the original Narset's Reversal.
Resolve the copy of Narset's Reversal, copying the original Narset's Reversal and returning the original Narset's Reversal to your hand.
Resolve the new copy of Narset's Reversal, creating a copy of Frantic Search and returning the original Frantic Search to your hand.
Resolve the copy of Frantic Search, looting twice and untapping Primal Wellspring and two other lands.
Repeat.

Infinite draw triggers

Infinite looting

Near-infinite magecraft triggers

Near-infinite mana lands you control can produce

Near-infinite storm count

Primal Amulet // Primal Wellspring

Frantic Search

Narset's Reversal

Activate Primal Wellspring and two other mana-producing lands by tapping them, adding at least {2}{U}.
Cast Frantic Search by paying {2}{U}, ensuring to use the mana produced by Primal Wellspring.
Primal Wellspring triggers, copying Frantic Search.
Resolve the copy of Frantic Search, causing you to loot twice, untap Primal Wellspring and untap the two other lands.
Holding priority, activate Primal Wellspring and two other mana-producing lands by tapping them, adding at least {2}{R}.
Cast Reiterate with buyback by paying {4}{R}{R}, targeting Frantic Search, ensuring to use the mana produced by Primal Wellspring.
Primal Wellspring triggers, copying Reiterate targeting Frantic Search.
Resolve both Reiterates, copying Frantic Search twice and returning the original Reiterate to your hand.
Resolve the first copy of Frantic Search, causing you to loot twice, untap Primal Wellspring and untap the two other lands.
 Activate Primal Wellspring and two other mana-producing lands by tapping them, adding at least {2}{R}.
Resolve the second copy of Frantic Search, causing you to loot twice, untap Primal Wellspring and untap the two other lands.
Repeat from step 5.

Infinite self-discard triggers

Reiterate

Cast Turnabout by paying {2}{U}{U}.
Holding priority, activate Primal Wellspring by tapping it, adding {U}.
Cast Narset's Reversal by paying {U}{U}, targeting Turnabout.
Primal Wellspring triggers, creating a copy of Narset's Reversal targeting the original Narset's Reversal.
Resolve the copy of Narset's Reversal, copying the original Narset's Reversal targeting Turnabout, and returning the original Narset's Reversal to your hand.
Resolve Narset's Reversal, creating a copy of Turnabout and returning the original Turnabout to your hand.
Resolve Turnabout, untapping all lands you control.
Activate Primal Wellspring and all mana producing lands you control by tapping them, adding at least {2}{U}.
Cast Turnabout by paying {2}{U}{U}.
Primal Wellspring triggers, creating a copy of Turnabout.
 Resolve Turnabout, untapping all lands you control.
Activate Primal Wellspring and all mana producing lands you control by tapping them, adding at least {1}{U}{U}.
Repeat from step 3.

Infinite magecraft triggers

Infinite mana lands you control can produce

Infinite storm count

Infinite untap of creatures you control

Infinite mana creatures you control can produce

Turnabout

Activate Primal Wellspring and another mana-producing permanent by tapping them, adding at least {1}{U}.
Cast Hidden Strings by paying {1}{U}, targeting Primal Wellspring and the mana-producing permanent.
Primal Wellspring triggers, copying Hidden Strings, targeting Primal Wellspring and the mana-producing permanent.
Resolve the copy of Hidden Strings, untapping Primal Wellspring and the mana-producing permanent.
Activate Primal Wellspring and the mana-producing permanent by tapping them, adding at least {U}{U}.
Cast Narset's Reversal by paying {U}{U}, targeting Hidden Strings.
Primal Wellspring triggers, copying Narset's Reversal targeting the original Narset's Reversal.
Resolve the copy of Narset's Reversal, copying the original Narset's Reversal targeting Hidden Strings, and returning the original Narset's Reversal to your hand.
Resolve Narset's Reversal, copying Hidden Strings targeting Primal Wellspring and the mana-producing permanent, and returning the original Hidden Strings to your hand.
Resolve the copy of Hidden Strings, untapping Primal Wellspring and the mana-producing permanent.
Repeat.

Hidden Strings

Activate an animated land by tapping it, adding at least {U}.
Cast View from Above by paying {U}, targeting the animated land.
Orvar triggers, creating a token copy of the animated land that is not a creature.
Resolve View from Above, returning it to your hand.
Activate the land token by tapping it, adding at least {U}.
Repeat from step 2.

Infinite landfall triggers

Infinite tapped Island tokens

Card That Animates a Land

Orvar, the All-Form

View from Above

Cast Nameless Inversion from your graveyard, as it is a Knight card, by paying {0} due to Primal Amulet and Morophon, giving a creature +3/-3 until end of turn.
If the creature has toughness 0 or less, the creature dies as a state-based action.
Repeat as desired.

Reduce any number of target creatures' toughness to 0

Reduce the toughness of opponents' creatures to 0 when it enters the battlefield

Haakon, Stromgald Scourge

Morophon, the Boundless

Nameless Inversion

Combos with "Primal Amulet // Primal Wellspring"