At the beginning of your upkeep, Thopter Assembly triggers, returning itself it your hand and creating 5 Thopter tokens .Sacrifice those tokens to Time Sieve to take an extra turn.
Cast Thopter Assembly for {6}.
Repeat for infinite turns.

Infinite turns

Lock

Thopter Assembly

Time Sieve

At the beginning of your upkeep, Thopter Assembly triggers.
Holding priority, activate Prototype Portal by paying {6} and tapping it, creating a token copy of Gonti's Aether Heart.
Gonti's Aether Heart enters the battlefield, causing you to get {E}{E}.
Resolve the Thopter Assembly trigger, returning it from the battlefield to your hand and creating five 1/1 Thopter artifact creature tokens.
The Thopters enter the battlefield, triggering Gonti's Aether Heart five times, causing you to get ten {E}.
Activate Krark-Clan Ironworks five times by sacrificing the five Thopters, adding ten {C}.
Cast Thopter Assembly by paying {6}.
Thopter Assembly enter the battlefield, triggering Gonti's Aether Heart, causing you to get {E}{E}.
Activate Gonti's Aether Heart by paying eight {E} and exiling it, causing you to take an extra turn after this one.
Repeat each turn.

Prototype Portal

Gonti's Aether Heart

Krark-Clan Ironworks

At the beginning of your upkeep, Thopter Assembly triggers.
Holding priority, activate Prototype Portal by paying {6} and tapping it, creating a token copy of Gonti's Aether Heart.
Gonti's Aether Heart enters the battlefield, causing you to get {E}{E}.
Resolve the Thopter Assembly trigger, returning it from the battlefield to your hand and creating five 1/1 Thopter artifact creature tokens.
The Thopters enter the battlefield, triggering Gonti's Aether Heart five times, causing you to get ten {E}.
Activate Ashnod's Altar five times by sacrificing the five Thopters, adding ten {C}.
Cast Thopter Assembly by paying {6}.
Thopter Assembly enter the battlefield, triggering Gonti's Aether Heart, causing you to get {E}{E}.
Activate Gonti's Aether Heart by paying eight {E} and exiling it, causing you to take an extra turn after this one.
Repeat each turn.

Combos with "Thopter Assembly"