Build help - mage slayer / witch hunter

[Darkzekkai]

I'm thinking of building a character who is made for taking down spellcasters. I was curious what class/race/background would work best for this idea. Obviously the mage slayer feat would be useful but what else?

[bid]

Shadow monk or rogue to get up close and personal quickly.

Halfling (brave) or elf (fey ancestry) for dex.

Lucky and mobile, I guess.

[tieren]

Level 7 oath of the ancients Paladin gets magic damage resistance aura, on top of charisma on all saving throws.

[Mad Puppy]

Assassin/Warlock Blade pact

You can move through shadows, Enter an area without your weapon then call it as needed.
Devils sight+Darkness
Hex+Sneak attack

Shadow Monk Bladelock also works

[mealar]

i've been building something like this recently, went with an eldritch knight with hand crossbow and full abjuration spells. idea is spend my slots on countering/cancelling his and shot him....alot

[Darkzekkai]

I've been looking at the deep stalker ranger from the underdark ua. It looks interesting. Nothing that particularly hurts casters but I like the ambush and hide style. And they get wis proficiency. And I was thinking wood elf for the race for their fey ancestry and the mask of the wild traits.

[Bloodcloud]

A mage slayer needs:
Mobility
High damage attack of opportunity
Stickiness

I reckon Swashbuckler rogue with sentinel might do the trick here.

[Felvion]

A witch hunter can be build by almost anything. It all depends on the playstyle you prefer. You could be a mobile, hit and run type assassin or a melee juggernaut that runs straight to the casters face and doesn't leave till he's dead. You could also be an "anti-caster" caster or someone who protects others from magic like a paladin.
For most of these themes the mage-slayer is almost worthless. Two out of the three benefits it gives require you to be in 5ft range from the caster. If you intend to utiliize the feat you should better make a character that would be able to stay within that range for as long it's needed.
I'd suggest a paladin. The mount can give you a lot of mobility although it's not always accesible (see dungeons or other narrow places). Heavy armor can help you defend against your enemy's minions. Smite and spells offer great dpr potential. The mageslayer feat makes sure that when you reach you enemy he won't be able to cast or maintain his concentration. He could at least try to disengage. If you are mounted it's almost hopeless. It would be completely hopeless if you had the sentinel feat too. As a human variant you could possibly have sentinel and mageslayer at level 4 if you are looking for an early game build. Your charisma (even with the standard array you could have a 14 from level 1) fuels your aura of protection and can help target some casters' weak spots (like charisma or constitution) from your spells.
Barbarians and fighters (especially eldritch knights with booming blade for early level lockdown) can make similar builds but their defence vs magic is lower than a paladin's.
Also don't underestimate the power of the lucky and alert feat. They could be very usefull in any witch hunter build. Lucky gives you advantage in crucial saves and alert makes sure you play before a caster strengthens his defenses,

[TrollCapAmerica]

Im pretty fond of Eagle Barbarians with Mage Slayer and GWM as another version of the things folks listed above. Your worst enemy with this is probably shield spells and the DM knowing what your doing

[Drackolus]

I've been really wanting to make a paladin/AT for a while. Lots of goodies in there.

Consider an Ancients paladin at 7 gets cha to all saves, resistance to spell damage, the ability to turn fey/fiends (summonable enemies) or restrain based on a physical save - and at 9, all paladins get Dispel Magic. Rogues get Evasion (esp. with the aura, you're basically immune to Fireball), uncanny dodge (which works for spell attacks!), and of course sneak attacks. Unfortunately, you'd be missing out on Counterspell unless you went to 14, and if you did that you couldn't get dispel magic. EK can get access to both (since they're abjuration). You could also go into Abjurer, with the free stacking temp health and super-counters at 10. If any build got you counterspell, if you can spare 2 levels into bard you could get Jack of All Trades and boost both without at 10-level commitment to Wizard.

If you really wanted to, you could just stick to Arcane Trickster for Spell Thief, but that's 17 levels. You could even use your 20th level spell to get dispel/counterspell and have both. Of course, that won't all be online for way too long.

[grimgold]

Oath of the ancients paladin seems the best if the wizard is compelled to stay and deal with you, otherwise the wizard could just leave. Dimension door and GTFO is a large enough problem that an erstwhile mage slayer is going to need some way to counter it or drop the wizard within a turn or so. Maybe an EK with counter spell and action surge?

[CantigThimble]

Bladelock seems strong here. He doesn't have the raw melee power that someone like a paladin or fighter does but he gets high level counterspells that prevent escape. A fey pact also gives you the best way to engage a wizard with a free spell slotless teleport+invisibility when you're attacked.

[Darkzekkai]

The ancient pally is looking pretty good to me. I was thinking my character would be more nature oriented. Probably a wood elf or half elf. I wonder if it would be acceptable to let him have ranger spell list? I've seen threads about letting ek use druid list and such. It would seem like ranger spell list would be the nature equivalent to the paladin spell list.

[solidork]

I think you might need Counterspell to even be a contender in the sort of meaningless white room scenarios I am imagining. Though I guess they can counter your counter so they can still Dimension Door. Is there a way to deny someone their reaction other than Shocking Grasp? Maybe your best bet is to try and one shot them with an Assassin?

[Corran]

I think you might need Counterspell to even be a contender in the sort of meaningless white room scenarios I am imagining. Though I guess they can counter your counter so they can still Dimension Door. Is there a way to deny someone their reaction other than Shocking Grasp? Maybe your best bet is to try and one shot them with an Assassin?
You can use subtle spell when counterspelling, so you cannot be counterspelled. That comes with a cost of 1 sp. And you get it by going sorcerer 3. That said, I dont expect many DMs will stick with countering counterspells tactics.

To the op. If you want to build a mage hunter, counterspell is the first thing on your list. Everything else is second to counterspell.