One idea to limit the power of the trolls is to work the ways players can move.
In order to kill someone in a melee game, you would first have to intercept, or catch up with them.
For example:
A traveler or tradesman moving goods between two player built towns/cities:
A horse drawn cart would move 15% faster than normal run speed. That means it would be difficult to catch/intercept on foot, and most likely you would only be able to get one hit on it before it travels away. This give a certain safety to the tradesman, and an attack would have to be coordinated to bring him down. Perhaps he could even whip his horses to get a momentary speed boost? Order them to run home without him? idk.
Horses:
Horses represent a potentially powerful trolling tool to kill random noobs and run away. Therefore, horses you can fight from, war horses should perhaps only be taken from a stables. A relatively expensive building you would normally protect within city walls. You would only have a warhorse with permission from the stables owner.
The thing here is that the randoming troll would then be under the responsibilty of someone higher up, i.ex a faction. So killing members from another faction could instigate diplomatic/political problems. This would be a self-governing anti-troll device.
Normal horses would also exist, but you cannot fight from them.
Personal "drop it all and run" speed bonus.
If you drop everything that can be used as a weapon from your inventory, you will run slightly faster than the fastest build possible "with a weapon attached."
This should make running away an option at all times, at the cost of loosing a tool or a weapon.
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Now, of course people will still raid, loot and troll, but it would require some organization on their part, as a group. A player could call up the warhorse equipped guard at the nearest friendly town, and they could again intercept the offending trolls/bandits.
