Dack's Duplicate

Once dethrone triggers, it doesn't matter what happens to the players' life totals before the ability resolves. You'll put a +1/+1 counter on the creature even if the defending player doesn't have the most life as the ability resolves.

Dack's Duplicate copies exactly what was printed on the original creature and nothing more (unless that creature is copying something else or is a token; see below), except it will have haste and dethrone. It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its power, toughness, types, color, and so on.

Haste and dethrone are part of the copiable values of Dack's Duplicate. If another creature enters the battlefield as or becomes a copy of Dack's Duplicate, it will copy whatever Dack's Duplicate is copying and have haste and dethrone.