Actually Morse Cave can be solo if u kill the monster fast enough.
In order to pass, one must have:
Gear:
Deviling Carded Garment (Either HBP or FAW) - there are tons of monsters inside the dungeon. 50% of neutral reduction makes u away from death.
Thanatos Spear with Hunter Fly Carded & Rideword Hat - for HP/SP leech
Imperial Spear - Abysmal Knight carded, high refine level(+7 or above) and with EA enchant will helps u a lot
between the period of defeating 
and the appearance of 
u need to kill certain amount of monsters in a limited time in order to continue. If u fail to reach the count, u will be kicked out from dungeon and teleported back to Prontera.
Any Fire Property Armor - The last boss spam metero storm so u need this. Although it also spam Jack Frost, the damage of the skill is pretty low and actually u can hardly be frozen since there are always monster around you.
Dark Blinder and Marduk Carded Headgear - sometime the boss summons some debuff monsters which keep giving you blind and slience.
Skills:
Vanishing Point main DPS against boss
Cannon Spear ranged AOE skill for killing the strengthened Archer Skeleton standing far away from you.
Overbrand not often used. Sometimes it is useful for clearing the mob around you.
Defending Aura very helpful for range attack damage reduce
Item: Fire Element Converter - the final boss is Earth 4, so...
These are the gears im using. Also standing on this position enables u to reach all monsters with cannon spear.
More Details are on the way xD
