Personality. The sword's purpose is to bring ruin to Vecna. Killing Vecna's worshipers, destroying the lich's works, and foiling his machinations all help to fulfill this goal.
The Sword of Kas also seeks to destroy anyone corrupted by the Eye and Hand of Vecna. The sword's obsession with those artifacts eventually becomes a fixation for its wielder.
Destroying the Sword. A creature attuned to both the Eye of Vecna and the Hand of Vecna can use the Wish property of those combined artifacts to unmake the Sword of Kas. The creature must cast the Wish spell and make a Charisma check contested by the Charisma check of the sword. The sword must be within 30 feet of the creature, or the spell fails. If the sword wins the contest, nothing happens, and the Wish spell is wasted. If the sword loses the contest, it is destroyed.
The Sword of Kas is a magic, sentient longsword that grants a +3 bonus to attack and damage rolls made with it. It scores a critical hit on a roll of 19 or 20, and deals an extra 2d10 slashing damage to undead.
If the sword isn't bathed in blood within 1 minute of being drawn from its scabbard, its wielder must make a DC 15 Charisma saving throw. On a successful save, the wielder take 3d6 psychic damage. On a failed save, the wielder is dominated by the sword, as if by the Dominate Monster spell, and the sword demands that it be bathed in blood. The spell effect ends when the sword's demand is met.
Minor beneficial property: While attuned, the wielder can cast Silvery Barbs. After casting roll a d6, on a roll of 1-5 you can't cast this spell again until the next dawn
Major beneficial property: While attuned, the wielder is immune to the following conditions: blinded, deafened, petrified, and stunned
Spirit of Kas. While the sword is on your person, you add a d10 to your initiative at the start of every combat. In addition, when you use an action to attack with the sword, you can transfer some or all of its attack bonus to your Armor Class instead. The adjusted bonuses remain effect until the start of your next turn.
Spells. While the sword is on your person, you can use an action to cast one of the following spells (save DC 18) from it: Call Lightning, Divine Word, or Finger of Death. Once you use the sword to cast a spell, you can't cast that spell again from it until the next dawn.
Sentience. The Sword of Kas is a sentient chaotic evil weapon with an Intelligence of 15, a Wisdom of 13, and a Charisma of 16. It has hearing and darkvision out to 2 range of 120 feet.
The weapon communicates telepathically with its wielder and can speak, read, and understand Common
You shape-shift into another creature for the duration or until you take a Magic action to shape-shift into a different eligible form. The new form must be of a creature that has a Challenge Rating no higher than your level or Challenge Rating. You must have seen the sort of creature before, and it can’t be a Construct or an Undead.
When you cast the spell, you gain a number of Temporary Hit Points equal to the Hit Points of the first form into which you shape-shift. These Temporary Hit Points vanish if any remain when the spell ends.
Your game statistics are replaced by the stat block of the chosen form, but you retain your creature type, alignment, personality, Intelligence, Wisdom, and Charisma scores, Hit Points, Hit Point Dice, proficiencies, and ability to communicate. If you have the Spellcasting feature, you retain it too.
Upon shape-shifting, you determine whether your equipment drops to the ground or changes in size and shape to fit the new form while you’re in it.
You blast the mind of a creature that you can see within range. The target makes an Intelligence saving throw.
On a failed save, the target takes 10d12 Psychic damage and can’t cast spells or take the Magic action. At the end of every 30 days, the target repeats the save, ending the effect on a success. The effect can also be ended by the Greater Restoration, Heal, or Wish spell.
On a successful save, the target takes half as much damage only.
You and up to eight willing creatures who link hands in a circle are transported to a different plane of existence. You can specify a target destination in general terms, such as the City of Brass on the Elemental Plane of Fire or the palace of Dispater on the second level of the Nine Hells, and you appear in or near that destination, as determined by the DM.
Alternatively, if you know the sigil sequence of a teleportation circle on another plane of existence, this spell can take you to that circle. If the teleportation circle is too small to hold all the creatures you transported, they appear in the closest unoccupied spaces next to the circle.
One creature that you can see within range must make a Wisdom saving throw. On a successful save, the target dances comically until the end of its next turn, during which it must spend all its movement to dance in place.
On a failed save, the target has the Charmed condition for the duration. While Charmed, the target dances comically, must use all its movement to dance in place, and has Disadvantage on Dexterity saving throws and attack rolls, and other creatures have Advantage on attack rolls against it. On each of its turns, the target can take an action to collect itself and repeat the save, ending the spell on itself on a success.
You gain the Invisible condition at the same time that an illusory double of you appears where you are standing. The double lasts for the duration, but the invisibility ends immediately after you make an attack roll, deal damage, or cast a spell.
As a Magic action, you can move the illusory double up to twice your Speed and make it gesture, speak, and behave in whatever way you choose. It is intangible and invulnerable.
You can see through its eyes and hear through its ears as if you were located where it is.
You ward yourself against destructive energy, reducing the damage taken by 4d6 plus your spellcasting ability modifier.
If the triggering damage was from a creature within range, you can force the creature to make a Constitution saving throw. The creature takes 4d6 Force damage on a failed save or half as much damage on a successful one.
Using a Higher-Level Spell Slot. The damage reduction and Force damage from this spell both increase by 1d6 for every spell slot level above 4.
You attempt to interrupt a creature in the process of casting a spell. The creature makes a Constitution saving throw. On a failed save, the spell dissipates with no effect, and the action, Bonus Action, or Reaction used to cast it is wasted. If that spell was cast with a spell slot, the slot isn’t expended.
Thunderous reverberations fill a 10-foot Emanation originating from you for the duration. Whenever the Emanation enters a creature’s space and whenever a creature enters the Emanation or ends its turn there, the creature makes a Constitution saving throw. On a failed save, the creature takes 3d6 Thunder damage and has the Deafened condition until the start of your next turn. On a successful save, the creature takes half as much damage only. A creature makes this save only once per turn. When you cast this spell, you can designate creatures to be unaffected by it.
In addition, you have Resistance to Thunder damage, and ranged attack rolls against you are made with Disadvantage.
Using a Higher-Level Spell Slot. The damage increases by 1d6 for each spell slot level above 3.
You create a sound or an image of an object within range that lasts for the duration. See the descriptions below for the effects of each. The illusion ends if you cast this spell again.
If a creature takes a Study action to examine the sound or image, the creature can determine that it is an illusion with a successful Intelligence (Investigation) check against your spell save DC. If a creature discerns the illusion for what it is, the illusion becomes faint to the creature.
Sound. If you create a sound, its volume can range from a whisper to a scream. It can be your voice, someone else’s voice, a lion’s roar, a beating of drums, or any other sound you choose. The sound continues unabated throughout the duration, or you can make discrete sounds at different times before the spell ends.
Image. If you create an image of an object—such as a chair, muddy footprints, or a small chest—it must be no larger than a 5-foot Cube. The image can’t create sound, light, smell, or any other sensory effect. Physical interaction with the image reveals it to be an illusion, since things can pass through it.
You can take the Hide action even when you are obscured only by a creature that is at least one size larger than you.
When you roll a 1 on the d20 of a D20 Test, you can reroll the die, and you must use the new roll.
You can move through the space of any creature that is a size larger than you, but you can’t stop in the same space.
You have Advantage on saving throws you make to avoid or end the Frightened condition.
When you are subjected to an effect that allows you to make a Dexterity saving throw to take only half damage, you instead take no damage if you succeed on the saving throw and only half damage if you fail. If any creatures within 5 feet of you are making the same Dexterity saving throw, you can share this benefit with them for that save.
You can’t use this feature if you have the Incapacitated condition.