Of all the faction stratagems I think the SK one is one of the worst and least used. It is not very diverse and seem fitted to a specific deck type. I personally like the MO strategem, but it seems unpopular and unused.
ST strategem is diverse and good.
NR strategem has superb niche use and is diverse too.
NG strategem is a good advantage and changes the way opponent plays.
SY strategem seems decent. It sees some use.
MO strategem seems good, but is generally not used.
SK strategem seems weird and not very popular.
Of the neutral ones, magic lamp seems to be the most popular, while many also stick with the traditional one (tactical advantage). Other than that it seems the other ones are more niche. Among them crystal skull seems most useful, and I've seen it used in various ways, so I think it's good enough. Cursed Scroll seems fine, and I've seen it used too. It's a "super mulligan".
That leaves us with basilisk venom and ceremonial dagger as the ones that seem to need a looking into. Ceremonial dagger is only 3 damage, which can be useful if you add other damage, but is it enough? All the other strategems have 4 or 5 value, while this one has 3.
Basilisk venom, I don't even know how to look at this. Poison a chosen unit would probably be a bit too much, but poison a random one is just bad. Poison seems to be valued at 1-2p by CDPR, so this is then the worst strategem by far, since it is also random. Random poison on 1 or 2 cards on the board is ofcourse not random, but doesn't really make up for it. I guess like NG strategem it will make the opponent change their opening plays, but is this overall good value?
So to sum it up..
Strategems that definetely don't need looking into:
ST, NR, NG, lamp, TA
Strategems that probably don't need looking into:
Skull, Scroll, SY
Strategems that may need reconsideration (due to low use):
MO
Strategems that need looking into:
basilisk, dagger, SK