hi, i just want to know if skill mastery and battle force (lvl 77 skills) are worth spending the sp?

Skill mastery gives a chance to use a skill without downtime, so it's important. What does that mean? You fire a skill and you fire it immediately again without waiting for the reuse. A double-skill.
It also gives a chance to double the duration of buffs. For example, let's say you have a th. You hit dash, it lasts 15 seconds. How would it be for it to last 30 seconds? It would be good.

Battle force... Well, not exactly. Maybe if you are an enchanter, such as sws, or something... It just adds some patk to the target, nothing exactly special. If you ask me, i wouldn't spend my sp on it unless i had plenty.