Weapon Enchantment +2
Markoheskir - the most powerful Quarterstaff
This weapon is the most powerful option for any kind of caster - Sorcerer, Warlock, Wizard. It provides everything that one would need - improved Spell Save DC, spell attack rolls, Weapon Enchantment, Arcane Battery, etc.
However, the most important one is Kereska's Favour which gives unique effects based on selected elements. Moreover, each of these elements comes with pre-selected spells that have no spell slot cost.
The most popular of these is Bolts of Doom, which unlocks Chain Lightning, hands down the most powerful offensive spell in the game. This does not cost you a spell slot, allowing you to even do some interesting multiclassing to optimize the builds.
Location - How to Obtain Markoheskir
The staff can only be obtained in Act 3, once you reach Lower City. First, your goal is to find a Sorcerous Sundries shop.
Before going there you need to make some preparations:
- Have a way to see invisibility - Volo's Eye, spell, or scroll See Invisibility, Area of Effect spells to reveal invisible objects
- Have a character with Arcane Proficiency - most likely a wizard, like Gale. They will have to reveal hidden plaques, levers, and interactable objects.
Once inside, go to the second floor, and you will be tasked to find the correct portal by a hologram. Choose the one on the left side:
Now, once you reach the tower, there will be a dialogue with Lorroakan. This relates to Nightsong, and for now what you choose only impacts companion approval and whether you enter combat. You can also not commit to any decision yet (tell him you will think about it), which will allow you to move further.
Once you are done with the dialogue you are free to explore the area. First, you need to reach the lower level. This can be done by jumping over hovering tables:
Now once below, walk around and there will be Arcana checks that reveal traps and various plaques. Look for a plaque, that says "Below", and activate the button nearby "Weave Button". It will take you down one more level. If you fail the checks, the button is at coordinates X:4962 Y: 719.
Once at this level, be sure to have someone with Arcane Proficiency and "See Invisibility" effect. There will be a d20 check for Arcane to pull the invisible levers.
Moreover, you can only activate the levers once, so be sure to save. If on Honour Mode, definitely bring someone with high Proficiency, cast Guidance, and any other benefits.
After you obtain the items, be sure to click the nearby button, which will teleport you back up. Now you have the most powerful staff in the game to be used on your caster.