Chromatic Star ability, paying ({1} magic symbol) , tapping it, and sacrificing it, adding ({1} magic symbol) .
Scrap Trawler triggers twice,
Myr Retriever triggers once, and
Chromatic Star triggers once.
Resolve the
Chromatic Star trigger, drawing a card.
Resolve the
Scrap Trawler trigger from
Myr Retriever, returning
Chromatic Star from your graveyard to your hand.
Resolve the
Scrap Trawler trigger from
Thran Dynamo, returning
Myr Retriever from your graveyard to your hand.
Resolve the
Myr Retriever trigger, returning
Thran Dynamo from your graveyard to your hand.
Cast
Chromatic Star by paying ({1} magic symbol) .
Cast
Myr Retriever by paying ({2} magic symbol) .
Cast
Thran Dynamo by paying ({4} magic symbol) .
Repeat.
Notes
This combo works by taking advantage of the fact that you can activate mana abilities during the declared activation of an activated ability. This allows you to delay putting the Trawler and Retriever triggers on the stack (and selecting their targets) until all permanents you need to target are in the graveyard. For more information, please see rules 605.3, 602.2b, and 601.2g.