Multiattack

The runeswarm can use Runecast. It then makes two cutting runes attacks.

Cutting Runes

Melee Weapon Attack: +11 to hit, reach 0 ft., one creature in the swarm's space. Hit: 15 (6d4) slashing damage, or 7 (3d4) slashing damage if the swarm has half of its hp or fewer.

Runecast

The runes swirling within the swarm form into the shape of a random rune, causing one of the following magical effects. Roll a d6 to determine the effect. 1. Algiz. The runeswarm magically calls 2d4 elk or 1 megaloceros. The called creatures arrive on initiative count 20 of the next round and defend the runeswarm. The beasts remain for 1 minute or until the runeswarm dies. 2. Dagaz. The runeswarm emits a burst of blinding light. Each creature within 20-feet of the swarm must succeed on a DC 16 Constitution saving throw or be blinded until the end of its next turn. 3. Ehwaz, Raido. A random willing target within 20 feet of the runeswarm gains the benefits of the expeditious retreat and freedom of movement spells for 1 minute. 4. Ingwaz. A random willing target within 20 feet of the runeswarm receives a brief glimpse of the immediate future and has advantage on its next ability check, attack roll, or saving throw. 5. Isaz, Kaunen, Sowilo, Turisaz. Fire, lightning, radiance, or cold winds swirl around the runeswarm. Each creature within 20 feet of the swarm must make a DC 16 Dexterity saving throw, taking 14 (4d6) cold (isaz), fire (kaunen), radiant (sowilo) or lightning (turisaz) damage on a failed save, or half as much damage on a successful one. Roll a d4 to determine the rune: isaz (1), kaunen (2), sowilo (3), turisaz (4). 6. Tewaz. The runeswarm glows with a baleful light. Each creature within 20 feet of the swarm must succeed on a DC 16 Wisdom saving throw or be frightened until the end of its next turn.