no tagging for anything. even just normal mobs in game. if you do dmg you will get credit for the kill for quest/loot.
events (including bosses) have a gold/silver/bronze tier system for rewarding exp/karma/gold/loot. which comes down to the amount of damage or time spent doing the event. gold tier is really easy to get. as long as you are trying to complete the boss/event you will get max reward. hitting the boss once then afk'ing wont get you credit.
there is no raid system for grouping, party is 5man in size. but i have gone to a boss solo with 100+ other people on a lower level char and still got full credit.
also when you go into a lower zone the game will auto adjust your level to the zones. some bosses are in lvl 15 zones so all the 80's get set to lvl 16 which reduces hp/def/dmg/ect. however a lvl 80 will still do more damage than a lvl 15 just not crazy amount like wow.
in PvP it will auto up level you to max 80 with your stats. WvW sets you to 80 but does not unlock your skills/traits. sPvP will put you at lvl 80 unlock all skills/traits, normalize gear, and give you access to all runes/sigel/weps.
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