Getting the most out of your caster (while leveling)

Can confirm this is still the case. However, be wary as Grease is pet and summon friendly but it's not party friendly, so it's good for solo play but if you're in a party with melee characters they are not gonna be very happy when you cast it on their feet.

Epic Areas
Necropolis
It goes without saying that Undead to Death is a handy spell in here, prep it as Maxxed, Empowered, and Silenced, if you can. Also, Control Undead on a Giant Undead Monk is incredibly useful as a tank to support your spellcasting. To defeat the spellcasters, the Necro'Sa, using Chain Lightning to disrupt their spellcasting. They do not have haste items so can only cast one spell per round. Use a Summons if you must but I usually save one as a backup when things get rough and you need to retreat. A Fire Elemental works well in here. Defeat the Dracolich to gain entry to the western gate via the Hetempka quest from the merchant at the Oasis. There are also a number of free rest areas in this dungeon that are useful to know. I can't recall the exact locations right now but one of them has an NPC lich in it that also hands out a new quest for you to tackle the Aquasabiats.

Open Desert & Canyons
Cliff fiends have a low fortitude so Wail of the Banshee and Finger of Death are highly effective on them. Prep a True Seeing so they don't Sneak Attack you. Asabiats you can keep as non hostile, which is what I recommend, by never completing the "Attempt for Peace" quest, unless you can negotiate a peace treaty without killing the Chief. Howver, to defeat these creatures use Bigby's Crushing Hand on the Warrior-Types, Bigbyu's Grappling Hand on the Archers, and Prep a few Spell Mantles for the Shamans, which will go down quickly with a Ball Lightning spell. They have mind immunity for some reason, I think it's inherent to their species so Hold Monster spells don't work on them as similar spells like Confusion or Fear.

Outkrata Labyrinth
Once you're able to access the Wester Gate you can fight Minotaurs. Shamans like to dispel you with Greater Dispelling, counter it with a Spell Mantle which will absorb the dispel. Minos have low fortitude saves so Wail of the Banshee is useful as is Finger of Death and Hold Monster spells, then use a summons to kill them. For the Rothe I just use a summons or IGMS.

The Beholder Caves
You may think that this area is impossible for a mage, but it's actually quite simple. You can use darkness spells to confound the beholders, but you can also use the ranged benefits of a Chain Lightning spell to kill them before they even see you. I encourage every spellcaster to try soloing these caverns as doing so can give you some great loot and xp rewards, especially since not alot of people like to go here because they don't want to get their buffs dispelled, which doesn't happen all too often.

Manonera City
It goes without saying an Air Elemental is useful here, as is Wail of the Banshee (just be sure to not Wail any kobolds or Moma won't be happy with you and then you will need to use a Charm Monster or Person spell on her to gain her favour back in order to continue quests or get the code for the day) and Fingers of Death. For defeating the spellcasters, again use a Spell mantle to absorb their Greater Dispel spell and then ball lightning to kill them. I think the Manonera are susceptible to fire so flame arrow works wonders on them or fireball. Acid Sheath works well on them too even though they have some innate acid resistance. For archers use a Hold Monster spell at a distance.

Manoner aCity Forgies Areas
For the spellcasters use a Spell Mantle to absorb their Greater Dispelling spell and then you can use a Greater or Lesser Breach to get rid of their spell mantles then Frost Arrow them to death. You can also Greater Dispel their aura if you want to, but it's not totally necessary. For the Forgies use a Bigby's Crushing Hand to stop them and then a Water Elementla to kill them or Ice Storm or Cone of Cold to kill them. For Gleeman you can use Bigby's Crushing Hand but it's not always successful. The way I deal with them is to breach their Etheral Visage so that the melees can attack them more thoroughly, and use a Water Elemental to tank them whilst you Frost Arrow them or Ball Lightning them.

I believe they only use Dispel or Greater Dispel. The only caster's I've seen that use Mordenkainen's Disjunction are boss type characters, like the lich in the NC Crypts, mini boss-type characters, like the dracolichs in the NC Crypts, and Magesmiths,. If they are using Mord's on you you're prettyscrewed, but toss up another spell mantle anyways and continue the good fight.

Additionally, it should be noted that Globe of Invulnerability and Lesser Globe of Invulnerability will also soak up a Dispel or Lesser Dispel spell. I rarely use Dispel myself because most of the casters will use a Spell Mantle on you. I prefer using Lesser Spell Breach against these types of casters.

Senduanta Spider Queen Portal Area
Someone else may be able to give furter insight, but from what I have been able to be witness to is that Wail of the Banshee works well in here against some of the spiders, your elemental smmons (fire I think works best) for the elder spiders, Cloud of Bewilderment will stun almost all the spiders (I think they have a weakness to the spell or something like that or it could just be poor fortitude saves), and IGMS. Do not use any Reflex Saving Throw spells as they have Imporved Evasion and high Reflex Saves so will take no damage from them. Ice Storm is another good option. Not sure how feasible this place is to solo as a mage, but it's fun to go down there with a nice group of peeps and farm them - they drop pretty great loot!