Put twice as many tokens/counters
Marath will enter the battlefield with 12 counters, because of this rule:


  121.6. If a spell or ability refers to a counter being “placed” on a permanent, it means putting a counter on that permanent while it’s on
  the battlefield, or that permanent entering the battlefield with a
  counter on it as the result of a replacement effect (see rule 614.1c).


If you use Marath's ability to remove all the counters, it will die before the abilty resolves unless you are increasing its thoughness in some other way. But you are right that it will get four times the number of counters you removed.