Terrifying Guise

Your familiar is cloaked in an illusory guise that makes it appear as a much larger and more terrifying creature. Choose a beast, monstrosity, or aberration with a challenge rating no higher than 8. The familiar takes on the appearance of that creature for the duration of the spell. The illusion is purely visual, but it is highly convincing, including appropriate sounds and smells.

While under the effect of Terrifying Guise, the familiar retains its usual statistics, but it can move the illusion to mimic the movements of the chosen creature. It can attack as though it were the illusory creature, though it uses its own attack rolls and damage.

When a creature within a 20 foot cone of the familiar sees the illusion, it must make a Wisdom saving throw against your spell save DC. On a failed save, the creature is frightened for the duration of the spell. A frightened creature must spend its turns moving as far away from the familiar as possible, and it cannot willingly move closer to it. When line of sight between the familiar and the frightened creature is broken,  the creature must repeat the saving throw. On a successful save, the creature is no longer frightened, but it still perceives the familiar as the illusory creature.

The illusion ends if the familiar takes damage, if the familiar dismisses the illusion as a bonus action, or if your concentration is broken. The illusion is immune to physical interaction and cannot be dispelled by normal means; it persists until the spell ends or is dismissed.