How to Unlock Most of Multiplayer Achievements in Singleplayer

https://www.nexusmods.com/mountandblade2bannerlord/mods/4587?tab=posts&BH=2
Download and install the Achievement Un(bloc)ker Mod from the Nexusmods.

Why I say this may work for limited time? Because maybe not longer work after some update of this game.

• Slice n dice

Kill 10 enemies with a successful chain attack combo.

Update: this one seems not work, I got it in multiplayer, you have to had the animation of your hand round your head

• Mounted Archery
  Kill 500 troops with range weapons while on horseback.
  This one works even faster than I expected, perhaps it counts your minions horse archery too.

• Lance-a-lot
  Kill 500 troops with a couched weapon while on horseback.

• Ride it like you stole it
  Spawning on foot, commandeer a mount and kill 5 enemy players without dying.

I unlock this by un-equip my horse and let my riders dismounted at the beginning of a battle, I mounted one of the horses and kill 5 got it.

• Roadkill

In battle, kill 100 enemies with charge damage.

• Headhunter

Kill 100 enemy players with headshots using ranged weapons in battle.

• Strike!

Kill 3 enemy players with a single mangonel shot.

Got it. In any siege, let your soldier shoot a mangonel first to get a AI-aimed direction, and you take over control of it.