Hi, le Baguette

Lust:
Lust has to be powerful it has to allow players to tare appart builings and all that jazz the only problem I see with lust is that it is so cheap players do not have to think about when to use it.
Players can afford always re-lusting everything without thinking twice.
I would thus propose to change the cost of lust from 50 to at least 100 mana making it a little more strategical to think about when to use the spell without reducing its effectiveness when it is.
Agreed something around 85 to not screw up orc vs orc game, keep some variability.
if 100 or more then orc wars will stuck at boring "timing attacks"
Heal:
Heal costs 4 mana per hit points healed a paladin has 90 hit points it means a full mana paladin cannot heal another paladin up as it will only heal 62 hp.
the cost makes it not worth it to even use the heal in combat or even else.
I would reduce it making it twice as cheap like 2 or even 1 so that it will most of the time heal up the unit you are using the spell on.
4 per HP ? good healing then

btw 4 mana per HP is Exorcism cost
Heal costs 6 mana per HP and maxed out using 240 mana at once = 40 HP
even if paladin had extra mana (over 240) u must click again to spend it. (Exorcism doesn't have that limitations, using all possible mana)
But idk how will Heal behave (do same 40 HP or dry same 240 mana) if cost = 2/HP...
Firebolt:
Coil is amazing, firebolt not so much. I would maybe lower its cost a bunch to make it more interesting to use it
Huh, Fireball? Isn't it?
Suggest 85 then, triple with full mana. and ready to use right from birth. A bit more fair against Coil - easy to miss, mostly not killing from 1 cast...
Unholy armor:
A very powerfull spell to make dk bombs and other fancy moves but it is very expensive overall still and could be a bit cheaper from 200 to something around 150 100.
Really? This costs 100 mana in original and good as it is. But here already 2 votes to decrease, hehe.
Polymorph:
A very powerful spell against other casters but it does cost a lot I would lower it from 200 to around 150.
Оh no pls, enough "click-click" stuffs in war2 already.
Flame shield:
A fun spell when used wisely I would however lower the cost of flames shield from 80 to something around 50
Some cases dropping that on enemy ogres crowd may worth it, but mostly blizz more easy and effective for 25 mana minimal.
But anyway 50 looks too good.
Much better to set minimal research cost for this, for exaple 500gold + same time cost as slow/haste (then do same for orcs 'raise dead'),
when that so easily accessible, player may consider use it rather or think for yourself what is better for current in game situation.