How to use these two spell skills correctly?

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How to use these two spell skills correctly?
I picked up this skill - the deadly spear - from the abandoned houses in the underwater village. According to the skill description, it can be thrown. But I have used it many times without any damage, and there are no corresponding spell effects. Is it necessary to use it with flying knives?
There is also a spell skill called deceleration, which is described as slowing down the target's movement and attack speed for a short period of time. However, I found that this skill also has no described effect or spell special effects when used.
I don't know if the production team didn't complete the production of these two spells.