Boomer Scrapper

Whenever this creature enters or attacks, you lose 1 life and create a Junk token. (It's an artifact with "{T}, Sacrifice this token: Exile the top card of your library. You may play that card this turn. Activate only as a sorcery.")
Whenever a token you control leaves the battlefield, put a +1/+1 counter on this creature.

Fallout

Whenever Boomer Scrapper enters the battlefield or attacks, you lose 1 life and create a Junk token. (It's an artifact with "{T}, Sacrifice this artifact: Exile the top card of your library. You may play that card this turn. Activate only as a sorcery.")
Whenever a token you control leaves the battlefield, put a +1/+1 counter on Boomer Scrapper.

Whenever Boomer Scrapper enters the battlefield or attacks, you lose 1 life and create a Junk token.
Whenever a token you control leaves the battlefield, put a +1/+1 counter on Boomer Scrapper.

Some spells and abilities that create Junk tokens may require targets. If each target chosen is illegal as that spell or ability tries to resolve, it won't resolve and none of its effects happen. You won't create any Junk tokens.

You can't sacrifice a Junk token to pay multiple costs. For example, you can't sacrifice a Junk token to activate its own ability and also to activate the second ability of Junk Jet.

You pay all costs and follow all normal timing rules for the card played from exile with a Junk token's ability. For example, if the exiled card is a land card, you may play it only during your main phase while the stack is empty.