Cayth, Famed Mechanist | Mana Echoes | Sword of the Paruns

Cards

You control at least one creature token.
You control at least four creatures that share a creature type with the creature token.
Cayth does not have summoning sickness.

Activate
Cayth by paying ({2} magic symbol) and tapping it, creating a token copy of a creature token you control.
When the creature token enters the battlefield,
Mana Echoes triggers, adding ({C} magic symbol) for each creature you control that shares a creature type with it.
Activate
Sword of the Paruns by paying ({3} magic symbol) , untapping
Cayth.
Repeat.

You may begin the combo with less creatures that share a type with the token, but you will need additional mana to do so until you begin to break even from
Mana Echoes' trigger. Once you have infinite mana, you may instead use
Cayth to get infinite proliferate.