Conjure Nest of Thorns

You summon 2d4 +2 ethereal ballistas. Each Ballista has hit points equal to 4d8 + your caster level+your Constitution modifier. Each ballista counts as a magical weapon for determining resistances and immunities, has an attack modifier equal to your proficiency bonus, a range of 150 feet, attacks twice, and deal 4d6 piercing damage on a successful hit.

Siege attacker. Ballista deal double damage to structures and objects.