This is my take on it.
Flavour Text
Magus Magic
You learn additional spells when you reach certain levels in this class, as shown on the Magus Spells table. Each spell counts as a sorcerer spell for you, but it doesn’t count against the number of sorcerer spells you know. These spells can’t be replaced when you gain a level in this class. Whenever you gain a sorcerer level, you can replace one spell you gained from this feature with another spell of the same level. The new spell must be an abjuration or a evocation spell from the sorcerer, warlock, or wizard spell list.
Magus Spells
Sorcerer Level | Spells |
---|---|
1st | Arcane Bulwark*, Arcane Brand*, Arcane Blade* |
3rd | Aid, Vortex Warp |
5th | Fireball, Phantom Steed |
7th | Freedom of Movement, Private Sanctum |
9th | Flame Strike, Wall of Force |
* New Spell
Arcane Warrior
At 1st level, you acquire the training necessary to effectively arm yourself for battle. You gain proficiency with light armor, shields, and all melee martial weapons.
Spellstrike
Also at 1st level, you gain early access to a unique Metamagic option, Spellstrike:
You can use this feature with no sorcery point cost, once you do so, you can’t use it in this way again until you finish a long rest.
Imbued Weapon
Starting at 6th level, you can spend a short rest focused on a weapon, and then count it as your imbued weapon until you use this feature again. The chosen weapon must meet these criteria:
If an imbued weapon is the material component of an Arcane Blade Cantrip, the spell is altered to have the additional scaling:
Counterstrike
Starting at 14th level, you gain the ability to counter incoming spells with your Imbued Weapon. If you are the target of any hostile spell you may use your reaction to make an attack with your imbued weapon targeting an AC equal to 12 plus the spell’s level. If you hit, the damage is applied to the spell-caster and they must make a concentration check with disadvantage or the spell fails.
If you succeed in disrupting a spell with this ability, you gain sorcery points equal to the spell level.
Signature Spell
At 18th level, you have achieved such mastery over a particular spell that you can cast it at will. Choose a 1st-level or 2nd-level sorcerer spell that you know. You can cast that spells at it’s lowest level without expending a spell slot. If you want to cast this spell at a higher level, you must expend a spell slot as normal. You also reduce the cost of any metamagic you apply to this spell: 2 points if it is 1st-level or 1 point if it is a 2nd-level spell.
Arcane Blade
Evocation cantrip
Casting Time: 1 action
Range: Self
Components: S, M (a melee weapon)
Duration: Instantaneous
The melee weapon you are holding is imbued with arcane power. You may make a melee attack with it against one creature or object within your reach. You can use your spellcasting ability instead of Strength or Dexterity for the attack and damage rolls of melee attacks using that weapon. You can increase the weapon’s damage die to a d10. The weapon also becomes magical, if it isn’t already.
Arcane Brand
1st-level divination
Casting Time: 1 bonus action
Range: 90 feet
Components: S
Duration: Concentration, up to 1 hour
You choose a creature you can see within range and mystically mark it as your quarry. Until the spell ends, you deal an extra 1d6 damage to the target whenever you hit it with a melee attack, and you have advantage on any contested Strength (Athletics) checks you make against it. If the target drops to 0 hit points before this spell ends, you can use a bonus action on a subsequent turn of yours to mark a new creature. At Higher Levels. When you cast this spell using a spell slot of 3rd or 4th level, you can maintain your concentration on the spell for up to 8 hours. When you use a spell slot of 5th level or higher, you can maintain your concentration on the spell for up to 24 hours.
Arcane Bulwark
1st-level abjuration
Casting Time: 1 action
Range: Self
Components: V, S, M (a suit of light armor)
Duration: 8 hours
An invisible protective magical force surrounds your armor until the spell ends. Your base AC becomes 13 + your Dexterity modifier. The spell ends if you dismiss the spell as an action. At Higher Levels. When you cast this spell using a spell slot of: 3rd or 4th level, your base AC becomes 14 + your Dexterity modifier; 5th or 6th level, your base AC becomes 15 + your Dexterity modifier; 7th or 8th level, your base AC becomes 16 + your Dexterity modifier; and at 9th level, your base AC becomes 17 + your Dexterity modifier.
So I wanted this to match Treanmonk's damage baseline. There is a bit of a blip up a 1st level and down at 5th.
The idea is that the Magus can be concentrating on Arcane Brand (a slightly nerfed hex or Hunter's Mark) and casting Arcane Blade (a melee version of Eldritch Blast) each round, to deal good damage.
The reason for Imbued Weapon is to gate-keep the extra attacks to 6th level so that dipping this class is not extremely attractive.
Arcane Bulwark addresses the main problem with Mage Armor whilst still providing some challenges: DEX is still very important; you have spell-slot tax for the day. With Shield Prof. I think AC is covered (but doesn't really get silly). The option of wearing some nice magic armor with secondary effects is good too.
Spellstrike is the nova button. I put the one free-use at first level just so I could get this in play early. Waiting until 6th level feels too long. It works a lot like Smite, but with the exception that you are actually smacking down with actual spells instead of boring spell-slots.
I'm not sure on the spell AC numbers for Counterstrike. Could do with a tweak.
I really phoned it in on the higher level spells for the Magus Spell-list.
I deliberately didn't build in solutions to HP or Sword and Board casting. Those solutions are already out there with feat and spell selections.