Essentially what @amessofamind said.
I see Norns as being PURELY FOR OFFENCE.
She goes nicely into a 3-2 or 4-1 yellow and purple stack when raiding against all the yellow/purple tanks which have one or both flanks as the opposite.
Norns effectively makes thosw enemies “weak” to ANY of the tiles you sling (yellow or purple)… Which is devestating to those defences as they are set up to DISCOURAGE a heavy stack against the tank colour.
Example:
Left Flank → Ursena
Tank → Guinevere
Right Flank → Seshat
If you stack 3 purple & 2 yellow against this defence (Norns as one of the yellow), you can target Guin and then make all three have weakness to BOTH yellow AND purple tiles… Effectively removing the whole point of that defence, which was set to make use of the “weak vs. strong” relationship that exists between yellow & purple…
Another example:
Left Flank → Drake Fong
Tank → Boss Wolf
Right Flank → Neith/ Joon etc…
Stack 3 yellow & 2 purples with Norns as one of your yellows. Same thing again. Target Boss with Norns special and suddenly the entire middle is weak vs. both yellow and purple tiles.
Example 3:
Left Flank → Vela
Tank → Telluria
Right Flank → Jean Francois
Stack a 2 Blue, 2 Red and 1 Norns. Targetting the middle three again and suddenly you get:
Telly weak to both the blue AND red tiles
Vela weak to the Red Tiles & neutral to blue
JF weak to blue & neutral to green
Essentially means you have no weakness tiles against the middle three enemies in this scenario…