I am somewhat confused by the wording of Alicorn Lance as stated in Elminster's Guide to Magic. The text states:
Casting Time: 1 action
Components: V, S, M (a lock of Unicorn mane)
Range: 120 feet
Duration: Concentration, up to 1 minute
A transparent alicorn (unicorn horn) forms about 2 inches from your brow. Starting the turn you cast this spell, for the duration you can use a bonus action during each of your turns to launch the horn at a creature you can see within range. The target must make a Dexterity saving throw, taking 3d6 radiant damage on a failed save. It is also outlined in silver faerie fire on a failed save, causing any attacks against it to be made with advantage until the start of your next turn. On a successful save the target takes half as much radiant damage, but suffers no other effects.
At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the amount of radiant damage increases by 1d6 for each slot level above 2nd.
I am confused about the supposed contradiction between "during each of your turns" and "launch the horn".
Does it return between launches? Does it reappear? Does it ever leave your head in the first place?
Can you launch a new horn each round?
Or is it just a single-shot effect that you can use on one bonus action that occurs during the spells duration?
I've added the full text: I was initially confused by the wording of when you can use it, but perhaps the additional details may help uncover intent.
In particular, I can understand the comparison to Spiritual Weapon, as it is also a 2nd level spell that does damage on bonus rounds for 1 minute. However Alicorn Horn does significantly more damage per turn (1d8 + SCM vs 3d6 save-for-half), has a range of 120 feet, and applies a (pseudo) status change.
On the other hand, it could be compared to Guiding Bolt, which is a level 1 spell, has the same range, does slightly more damage (4d6) and also applies a (pseudo) status change. However, it is also a ranged spell attack (misses miss) and applies the advantage only to the next attack before the end of your next turn (as opposed to any attacks)
Note that upcasting spiritual weapon takes 2 levels per dice of additional damage; alicorn horn updates 1 level per dice. Effectively, if it can be read as an attack per turn, it turns a 3rd-level slot into 10 bonus-round-usable, slightly powered up, still allowing spells on actions, level 1 guiding bolts!