Twilight Knife and spell attacks

[Andruxu]

About https://www.d20pfsrd.com/magic/all-spells/t/twilight-knife/

Does the wizard have to make a physical attack, or can he cast offensive spells instead?

[Azothath]

→ Twilight Knife:K3
Physical, spell(cast or wand etc), SLA, SU attacks may qualify. Melee attacks, Ranged attacks, Touch attacks, Ranged Touch attacks are all attacks(d20 roll) but many spells are certainly attacks (see invisibility spell). You need to attack ONE target to make this spell effect trigger.

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Home Game Twilight Knife:K2 {rework}

→ How to play a Wizard, 10-2024

[Andruxu]

What happens if I change targets? For example, if in one round I attack a creature 30 feet to my left, and in the following round I switch targets and attack a creature 30 feet to my right? Does it stay where it is, or does it rematerialize on the new target and attacks?

[Joynt Jezebel]

As I read the spell description the twilight knife will move to attack the enemy you do if it can. So it moves rather than dematerialise and rematerialise.

I expect circumstances where this can't be done, per the description, are those where there is no physical path big enough for the dagger to move to the new target.

[Azothath]

from the spell, "You create a darkly sinister floating knife that attacks the same creature as you each round.... Unless you specifically will it to do otherwise, or it proves impossible to do so, the knife always maneuvers itself so that it can flank your opponent before making the attack."
so it floats about within close range of the caster but does not occupy a square. It is a spell effect. There's no Fly speed so it can cover the usual hemisphere of close range radius.
In a technical way it can attack any target within close range with line of effect. It does not need an extra square to attack from.
If you shoot a ray (ranged touch attack) beyond close range then the twilight knife cannot attack that target.
It does not work with a summons as that does not count as you making an attack. Again, see invisibility.
As written, the knife does not confer a flanking bonus to the caster (the spell does not say it does, nor is there a flanking bonus for the knife written into the attack... but many GMs will give it the +2 flank bonus if it applies).
Getting to apply the sneak damage is going to be rather rare.

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in a practical game manner - use a different spell. This spell is woefully underpowered (compare it to any 3rd standard spell like aqueous orb, swarm of fangs, displacement, fireball, lightningbolt).
An arcane caster has no business being in melee combat. This spell will just make them want to kill the caster faster. Even for a Ninja X Wiz 1 with a wand this spell is bad as it is not a flanking buddy.