Current build:
100 Magery
100 Eval
100 Mysticism
100 Focus
100 Spellweaving
100 Meditation
120 skill I'm mulling over -
Fighting overland mobs right now (Oni Point on Homare) - so I use:
Rising Colossus - getting a lot of fizzes so likely going to work on 100+ scrolls once I get the $$
Once the RC engages I'll start hitting the mob with Plague (Myst) followed by E-bolt (Magery) or Bombard (Myst) - toss in an occasional Flamestrike depending on resists - then use Word of Death from Spellweaving. And heal myself with Cleansing Winds or Greater Heal...
Sound about right or am I missing a combo that would work. So many spells to choose from
Any advice is appreciated!
Pure generally means 'one school of magic'.
You are missing how this works.
Take your example monster - Oni - they are vulnerable to Demon Slayer, so you should be holding a Demon Slayer spellbook.
There is no SDI cap for PvM so you can overload this to your hearts content.
Next it's resists are highest in physical/fire/poison and lowest in cold/energy. You can have one Colossus doing physical damage, or two Energy Vortex's doing energy damage, I'm assuming your SDI is fairly low if you're relying on summons for distraction as normally it isn't needed to kill an Oni with spells.
All schools of magic (despite it not being explicitly stated in their respective books) have their spells in circles, the circle essentially means the cast time (longer = more chance of being interrupted, unless you are playing in Protection, in which case you should just use the highest damage spell for the monsters weakest resist), mana cost and damage of that spell. For example Meteor Swarm/Chain Lightning are both 7th circle, they have the same cast time, mana cost and damage, the only difference is that one hits fire resist and the other hits energy resist, so if the target has weaker energy than fire resist then that spell will do more damage.
Mysticism has the high damage 7th circle spell Hailstorm - cold damage - which Oni are weakest against. Mindblast is also cold damage and casts faster than Energy Bolt/Bombard as it is a lower circle, Bombard is a physical damage version of Energy Bolt so not particularly useful against a monster with high physical resist. (Bombard also has the potential to briefly paralyse a target, however, this is calculated against the targets resisting spells and is unlikely to be useful against anything worth fighting.)
Unless you have 4/6 casting Word of Death is a very slow cast and with more SDI and the right spell choices you could most likely out damage it with normal spells in the same time frame.
Spellweaving and Mysticism are heavily defensive skills that add little to fast combo kills for overland monsters that generally die in 2-3 hits anyway.
Compare this to a Necro/Mage attacking the same monster:
In Wraith Form - so you are never out of mana as you leech it all back.
Corpse Skin - lower it's fire/poison by 15 (it puts phys/cold up 10, but this is still better overall than the Mystic attacking due to the spells you can use)
Flame Strike/Evil Omen combo - cast this way around, the Omen casts fast enough to land before the damage from the FS, and boosts it's damage by 25%
Omen off of Chain Lightning also - giving you high damage coverage of the main weaknesses monsters have.
Fast casting spells to finish red lined targets - Pain Spike/Wither
Apart from Wither the above can be done with 60 Necro/60 Spirit Speak - giving you spare points to strengthen the character in other areas.
Your current template lacks any synergy of skills, as in they don't compliment each other well for any particular purpose, and are very much playing a jack of all trades master of none type of template. Hybrids are fun but try restricting it to two schools of magic and making the character stronger overall. For example, you could drop the Spellweaving and add Inscription - this would give you more spell damage with your Magery spells and some innate Casting Focus (5 iirc) to prevent you getting interrupted as much. Or you could drop Mysticism/Focus and pick up a Bard skill, Provoke monsters to fight each other, or Discord to drop their resists and skills these also come with powerful Masteries, the Discord offensive Masteries can even be set to attack the resist of your choice. Or if not a Bard skill you could fit Taming in there. Or warrior skills.
Mysticism doesn't really offer a lot for the amount of skill points it requires. It's best spells are:
Enchant - on very specific dexxer builds
Stone Form - defensive - works best on a dexxer
Cleansing Wind - defensive - slow cast time
Healing Stone - defensive - very good! Like carrying Greater Heal potions and 50 EP
Spell Trigger - imo best used for an emergency Cleansing Wind
Hail Storm - offensive - cold damage version of any 7th circle spell
...Rising Colossus - offensive - slow, takes all slots, physical damage, less coverage than two summons
All of the other Mysticism spells are pretty useless as they are either void damage (hit a random resist) or are less favourable damage type versions of spells you already have with a more complete magic school. For example, Eagle Strike, why would you want an energy damage version of Fireball if you can already cast Lightning/Energy Bolt to cover that damage type.