Roar of the Kha is exiled with a kick counter on it.
Zethi and Aphetto Alchemist do not have summoning sickness.
Creatures you control can tap to produce at least ({4} magic symbol) ({W} magic symbol) .
Steps
Declare Zethi as an attacker, triggering its second ability.
Holding priority, activate all mana producing creatures you control by tapping them, adding at least ({4} magic symbol) ({W} magic symbol) .
Activate Lithoform Engine's first ability by paying ({2} magic symbol) and tapping it, copying Zethi's triggered ability.
Resolve the copy of Zethi's ability, creating a copy of each card exiled with a kick counter of it and causing you to pay ({1} magic symbol) ({W} magic symbol) to cast the copy of Roar of the Kha.
Resolve the Roar of the Kha copy, untapping all creatures you control.
Activate Aphetto Alchemist by tapping it, untapping Lithoform Engine.
Repeat from step 2.
Once you have infinite mana, you may use that mana to then cast the copies of all other cards exiled with kick counters on them.
Results
Infinite casts of all cards exiled with kick counters on them.
Infinite magecraft triggers.
Infinite mana creatures you control can produce.
Infinite mana nonland permanents you control can produce.