Is there something like BGT for Icewind dale ?
or a mod that ports IWD 1 to IWD 2 standards ?
I don't think there is any, as they have vastly different game rules and interface. IWD is 2E (with expansions it becomes a somewht 2,5 E) while IWD2 uses 3E rules (mostly) so it is kinda impossible.
Further, the player party in IWD 1 is not the party in IWD 2, story wise the events take place in a few decades later in IWD 2 and there is only one small plot device which ties the story to IWD1's main villain. You can learn about IWD 1 party's adventures and fame from a psychic woman at the start of IWD 2.
Strangely enough, there was mod which let you play BG2 in IWD 2 engine and rules, with all spiffy 3E feats and rules and shit. It was called Ice Wind Gate and it was buggy as hell and was destined to stay beta AFAIK.
I'm kinda starting to dislike the caster 'improvements'. Many mages that I encounter have this undefeatable combo of Globe of Invulnerability + Mirror Image + Prot from Arrows (which stops all arrows in my game) and open up with full-party disabling spells, resulting in at least one death and probably more. This would be fine if I had some way to remove these protections. A low level party does not have access to these (no breach since it is lvl5, dispel magic with a too low caster level to have any effect) and have no option but to die en masse.
Don't install the component that makes protection from missiles blocking magical arrows as well, it does not make sense rules wise. It is a lvl 3 spell, it should not be powerful enough to render the caster invulnerable to all missiles in game world. You can, however install the component which makes all relatively easy to find +1 ammunition to masterwork, hence you will need hard to find +2 ammo to hit those mages.
As for strategies, retreating to a different area is cheesy. Here are a few ideas isntead:
-Cast Spell thrust or Secret Word to take down the Globe of Inv. If they are improved invisible you can not target them, however mods also change Secret Word and the like to be area-effect spells. Once MGoI is down you can dispel their invisibility/ghost armor via Detect Invisible/Illusions spells and hack away easily.
-A thief with %100 Detect Illusions skill is extremely valuable against spell casters. Let the thief detect traps near heavily illusioned enemy and he will dispel his illusions:mirror images are gone, Improved Invisiblity is blown so mage loses AC and to hit bonuses as well as can now be targeted by spells:Also if spell revisions are installed ghost armor is also an illusion which gives huge AC bonus, it is gone too. Also, a trick with detect illusions. Pause the game, have the thief attack the mage and then press detect traps. The thief will both attack and detect illusions at same time.
-BG1 mages do not have Death spell, so summon monster via spell or wand, or animate dead and let the summons attack the mage while your party retreats a few screens away. Hopefully, mage will waste his minute meteors or spells on summons and even summons can get a lucky critical on them.
-Arrows of dispelling:while rare and/or costly and some mods even erase them from stores, give them to Kivan or Coran and they will insta-destroy a mage's buffs and kill him in the next few shots. (which you should switch to normal arrows, or flaming arrows for that extra satisfaction of burning)
-Biggest threat is Confusion (or its bigger, badder brother Chaos, for high lvld mages in BG1) spell, if your party is hit by it in the middle, you will lose control of your party members, they will attack each other and you will have many casualties if not a TPK. So send Minsc or another character with berserk/rage ability and have him/her rage when the spell hits him/her only (your party should be in a safe distance) or potion of clarity or magic protection works too.
-If you have Confusion spell, cast it! It can not be stopped by Minor Globe of Invulnerability, and a confused mage will wander around and occasionaly attack, never using scripts to cast spells. Though mages have good save vs spells, they can still fail their saving throw.
-Keep mirror images and shield spell on characters that can cast them (even bards) cause a minor spell trigger with two magic missiles hurts a ton! (20-50 damage is hardcore at low levels)
-Always have a few charm spells handy, when the enemy mage charms your fighter, immediately charm them right back! Also, charm spells are very useful, if you are fighting a group, use them on fighter types! (unless they have gulped a magic protection potion) Charming a mage in an enemy group is difficult since they have good saves, but if they don't hage MGoI, go for it:You can then use all of their spells to wreak havoc on their allies.
-Potions of magic shielding/protection/invulnerability are very useful, but careful as they can get dispelled. Hence, first send a buffed character so the mage will dispel his useless buffs, retreat the character and send in the one with Magic protection potions in his belly. Viconia is also perfect since she has natural MR.
-Protection from magic scroll:no mage can touch you in BG1. There are quite few to be found and/or purchased in game, and they make even the most dangerous mage battles a walk in the park. I used one on Ice Island, sent my protected fighter in fray and butchered all those crazy high level mages with ease. Otherwise that place can be painfully difficult.
-If you don't have an inqusitor bards with dispel/remove magic are useful since their caster level is high, they can take down mage protections better than mages in your party. Brave, brave Sir Garrick may not be as useless as people think. (he still sucks a lot, though)
-Tiax's ghast summon is overpowered. If it can get a scratch on a mage, the said mage will most likely fail his saving throw (mages have bad save vs death stuff) and will be paralysed which equals death. Mods also put Tiax to Beregost so you can get him earlier.
-Some tougher mages will have Fire Shields on. Do not try to melee them unless you have total immunity to the fire/cold damage it deals. Use missile weapons until fire shield is down.
-Insect Plague spell totally rips mages apart, distrupting their spell casting, eating through their mirror images, stoneskins, and damaging them. Once you can cast this spell BG1 mages are super easy. (ie:if your PC is druid, or you have Faldorn, or if Jaheira is really high level)