Magic Resistance. The House Elf has advantage on saving throws against spells and other magical effects.
Counterspell (Recharge 6). As a reaction, the House Elf can interrupt the casting of spells within 50ft. Spells of Level 2 or lower automatically fail, otherwise the House Elf must make a WIS check.
Magical Retaliation. As a reaction to being harmed by a creature it can see, the House Elf can trigger a Wild Magic Surge in the creature. Spell Level 2, DC 13.
2x Arcane Blast. Spell Attack. +5 to hit.
Hit. 6 (1d4+3) Force damage.
Duelist. In lieu of one extra attack, the House Elf can add 4 (1d6) to the damage of their attack and force a save against one of the following conditions.
Disarm, DC 13 STR save. Failure by five or more and the House Elf grabs the weapon.
Prone or Push. DC 13 DEX save, Failure to beat a 13 gets both.
Parry. House Elf gains Disengage and adds 3 (1d4) to it's AC.
Distracting Strke. DC 13 WIS save. All attacks against victim have advantage until end of House Elf's next turn. Failure to beat a 13 grants disadvantage on saves.
Taunt. DC 13 CHA save. Target cannot move beyond 70ft from the House Elf until the end of their next turn.
Gut Worms. DC 13 CON save, or target is Poisoned until the end of the House Elf's next turn.
Grovel, Cower, and Beg. (Recharge 5-6) As an action the House Elf can cower pathetically to distract nearby foes. Until the end of their next turn, their allies gain advantage on attack rolls against enemies within 10 feet of you that can see.
===Reactions===
Mage Slayer. The House Elf may make an Opportunity Attack if a creature casts a spell within 35ft of it. The creature must make a Concentration check vs half the damage for the spell to succeed in casting.