StoriedStoried is a static ability. It means “Any time you control three or more permanents that are artifacts, Sagas, and/or legendary and you don’t have an enduring story, you have an enduring story for the rest of the game.”
Enduring story is a designation that has no rules meaning other than to act as a marker that other rules and effects can identify. Any number of players may have the enduring story designation at the same time.
After a player gets an enduring story, continuous effects are reapplied before the game checks to see if the game state or preceding events have matched any trigger conditions. (CR 702.195) (If you control three or more artifacts, legendaries, and/or Sagas, you have an enduring story for the rest of the game.)
Whenever Bifur enters or attacks, put a +1/+1
counterTo counter a spell or ability is to cancel it: remove it from the stack without resolving it. A counter on an object or player is instead a marker that changes characteristics or interacts with rules or abilities; for example, a +1/+1 counter modifies a creature’s power and toughness. (CR 701.6; 122.1) on target creature.
As long as you have an enduring story, if a triggered ability of a Dwarf you control triggers, that ability triggers an additional time.