how you beat the octocupus?

[Gatts]

The point is to provoke kraken so he won't be spawning devilfish - standing just before his main tentacle will do this - (it does not work always, but still often enough - so you have much more "free" rounds when he damages only your "provoke him" unit instead of summoning zounds of devilfish)

Other way around is to have thonrs - use the dead devilfish for new thorns - populate most of the battlefield with such summoned devil, so you gain:

1.) use the summoned thorns as provokative unit - win win situation
2.) if devilfish are summoned - if not free spaces are available - they won't be summoned - octopus loses one turn
3.) thorns are cheap and easy to get (mostly in Darion)

or use Similar strategy as for the turtle - get DMG resistant unit - (ghosts) (cheaper than castin god's armor - which is expensive, lasts only few turns, hard to get) and cast on it archmagi "shield" - another 50% less DMG - if you are lucky, you have stoneskin - increasing phy res as well DEF (phy res is not cumulative... ) - place this unit direct in front main tentacle - use the rest 3 slots for archers and shoot it down (even if the octopus will summon devilfish you will shoot em down)
Do mind that with good enough ATT/DEF your ghosts can last "alive" for very long time - the actually can replenish themselves from fighting octopus (or even better - they get hit by octopus, but can steal life from devilfish - but you should be very cautions how you handle them - on impossible level your limit of ghosts jumps over 100% leadership - and they will fight you instead)

I used thorns + ghosts nearly always when fighting octopus... (2 stacks ghosts, 2 stakcs thorns... on shooter) - if you are lucky - you can get some cool shooter like alchemist (only 3 hexagons range, but in that battlefield it is very usefull) or canoneers (creepy fast)... or when you already have undead in army - use skel archers...
Don't be afraid to use any archers - even human - even if you are not paladin with "tolerance" skill - -20% is not that bad (in normal HOMM you would lose control over them - they would lose turns in combat... having lover att/def/critical is not such big deal)
Archmages can cast shield - but they don't deal such nice damage on shooting.