[Boron]

summary :
5 types of strategical attack spells :

type 1 : ghost rider type .

an independent army attacks the chosen province .
after the battle the independent warriors disappear no matter if you won or lost .

type 2 : troops under own command type .

your troops attack the chosen province . this can be either summons ( call of the wind etc. ) or your own troops ( teleport / astral travel ) .
if you win you are either sieging the province or you take over control when there is no castle . if you loose your whole army is annilihated if you don't have at least one direct neighbor province to your chosen attack province .

type 3 : damage spells type

you inflict damage on one or more randomly chosen targets in the chosen province via damage spells ( seeking arrow etc. ) .

type 4 : assasination attempt spells

only 2 such spells come to my mind , manifestation and earth attack . they are for many nations not main research priority so by the time you get these 2 spells 1/3 - 1/2 of the possible targets will already be sc's / strong battle mages with guards . against these your assasinators have bad odds .
the other 2/3 - 1/2 of possible targets are priests or researchers which are kinda cheap (50-150 gold class ) .
so in general these spells have a very bad RoI .
but no rule without exemption :
if you know that there is only one leader in the province on which you want to send the assasinator ( e.g. a sc ) you can perhaps send several earth attacks on that province .
hp are only restored after all battles .
so perhaps 2 earth attacks are just enough to kill the target .
but in general teleporting in your own sc or attacking with ghost riders gives you higher better results for less gems .

type 5 : the various kill population / increase unrest / create misfortune / create gold loss rituals

examples are blight , tidal wave and the like .
all in all under this type fall about 10-15 battle spells . some are available early game , some midgame and some lategame .
all have in common that they "only" do damage on the province , but not on the units in the province .
for blood hunters they can be a real problem though .
i mentioned them only for the sake of completeness but they are no important part of my guide .