1 Natheless the enchanter would not spare his pain,
Natheless > Nevertheless pain > efforts
2 In hope to win occasion to his will;
win > persuade, subdue, seize; hence: shape occasion > circumstances
3 Which when he long awaited had in vain, 4 He changed his mind from one to other ill:
other > another; the other
5 For to all good he enemy was still.
still > ever, always
6 Upon the way him fortuned to meet,
him > (The same construction is found at 102.12:5-6; Archimago is the object of "meet"; the knight is the subject of "fortuned")