Draugr

Curse of Undeath. A slain draugr will rise again within the next 24 hours unless its accursed body is destroyed (e.g. decapitated and/or burned). 

Earth Glide. The draugr can burrow through nonmagical, unworked earth and stone without disturbing the material it moves through. 

Spellcasting. The draugr is imbued with dark magic that allows it to intermittently cast spells using its Trollskap ability. Its spellcasting ability is Constitution (spell save DC 13, +5 to hit with spell attacks). 
Level 1: bane, ray of sickness
Level 2: darkness

Multiattack. The draugr makes two longsword attacks or two longbow attacks. It can use its Life Drain in place of one longsword attack.

Life Drain. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 5 (1d6 + 2) necrotic damage. The target must succeed on a DC 13 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Longsword. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) slashing damage, or 7 (1d10 + 2) slashing damage if used with two hands.

Longbow. Ranged Weapon Attack: +4 to hit, range 150/600 ft., one target. Hit: 6 (1d8 + 2) piercing damage.

Trollskap (Recharge 6). The draugr casts one of its spells.