Guild Wars 2

How does the damage work from Conditions if it comes from multiple sources?

ex: Player 1 applies Poison for 10s with 1000 Condi Dmg and Player 2 applies Poison for 10s with 1500 Condi Dmg, How will the game calculate the Dmg done of the poison?

It depends on the order and timing for the applications. For example, if player 1 applied his poison, then 5 seconds later, player 2 applied theirs, then for the first five seconds it would be Player 1 ticking for 180 damage, then for 10 seconds it would be Player 2 ticking for 230, then for 5 it would be Player 1 again for 180 (the remaining duration).

Whenever a new stack of Burning, Fear, or Poison gets applied, it puts all prior stacks on pause until it either runs its course or gets paused by a new stack (or the condition gets removed).