ATaleOfTwoBrothers
From The Battle for Wesnoth Wiki
First scenario:Easy recruit a bunch of units and attack use spermen and maybe a few bowmen to smash the undead leader.
Second scenario:A bit harder you should use horsemen to deal with the elves then spermen and bowmen to kill the undead leader.Take the help from the level 3 heavy infantry man.
Third scenario:Recruit alot of heavy infantry and recall any experienced units.After the fight get aren to bjarn(he is hidden in the cave).
Fourth scenario:Um....