How are warlocks viable at higher levels?

Question

This is in D&D 5e, specifically the starter adventure they sell.

I'm just getting started and I am interested in the Warlock class. From reading a bunch on this class it seems like the easiest way to play one is as an Eldritch Blast spammer. I understand the damage output can be quite high.

However, in 3rd edition, from what I remember, higher level monsters frequently had resistance to spells below a certain level. This would make EB unviable. Furthermore, with so few spell slots, seems like at this point the Warlock won't be useful in combat any more against those monsters. I understand that not all encounters will play out like that, but it's a pretty big deficiency. Does this happen in 5e? If it does, how can the Warlock remain viable at higher levels?

Answer 1

Warlock is as viable as other classes

So, let us start by your assumptions:

it seems like the easiest way to play one is as an Eldritch Blast spammer. I understand the damage output can be quite high.

This is right. While it is not the only way to play it, it is arguably the easiest and, as this answer shows, a very viable choice.

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Now, let us go to the problem I see you are having:

However, at mid to high levels don't enemies start having resistance to spells below a certain level, making EB unviable?

No. In 5e, the way monsters get magic resistance is the following:

Magic Resistance. The creature has advantage on saving throws against spells and other magical effects.

Note that Eldritch Blast is not a saving throw inducing spell, it is a Ranged Spell Attack, and is, therefore, not affected by it.

The other way monsters get to resist to effects are:

• Resistance or immunity to a type of damage. Eldritch Blast does Force damage, which is the least resisted type of damage.

• Legendary Resistance. Some enemies can automatically succeed a saving throw. Again, this does not matter, as EB is not a saving throw inducing spell.

Overall, EB will be as effective in high levels as in low levels, and you will not, in any moment, become useless in combat.

Edge Cases

There are some encounters which will make EB useless. From my head, I can think on 3, all of them quite unlikely.

The Helmed Horror is immune to force damage, and, to the best of my knowledge, there is no way to bypass this immunity. From the 3 monsters, this is possibly the one more likely to be met in a regular adventure - even appearing in the published Princes of the Apocalypse. You should avoid this encounter, if possible.

The Rakshasa is immune to spells of 6th level or lower. This is a CR 13 monster, so it is pretty much a screw all spellcasters, not specific to Warlock, but Warlock will be the one most screwed by it. But then again, it is one specific creature among hundreds of others.

And finally, the Tarrasque. It has the Reflective Carapace feature, which states

Reflective Carapace. Any time the tarrasque is targeted by a magic missile spell, a line spell, or a spell that requires a ranged attack roll, roll a d6. On a 1 to 5, the tarrasque is unaffected. On a 6, the tarrasque is unaffected, and the effect is reflected back at the caster as though it originated from the tarrasque, turning the caster into the target.

So, yeah, Eldritch Blast is useless against a Tarrasque. But hey, so is resisting. Just let it devour you, your friends and the world. Jokes aside, while it is an extremely iconic monster, it is also unlikely your choice of class and build should be made around it, because you are not likely to encounter it any time soon.

Answer 2

Immunity to spells up to a certain level is an extremely rare mechanic

In fact, there's only one "generic" creature I can think of off the top of my head that has this property, and that's the Rakshasa, which has the special quality:

Limited Magic Immunity. The rakshasa can't be affected or detected by spells of 6th level or lower unless it wishes to be. It has advantage on saving throws against all other spells and magical effects.

A few other boss monsters, like Tiamat (from the Rise of Tiamat module), have the same Limited Magic Immunity quality. The Tarrasque has an interesting variant where it is simply unaffected by (or possibly reflects!) any spell attacks (or line effects), which makes it functionally immune to a large set of spells including eldritch blast. These are however unique boss monsters which are meant to be extremely challenging to fight, and their unusual resistance to magic is part of what makes them unique.

Some creatures are immune to specific spells, such as the helmed horror:

Spell Immunity. The helmed horror is immune to three spells chosen by its creator. Typical immunities include fireball, heat metal, and lightning bolt.

And many powerful creatures have some degree of magic resistance, such as the helmed horror's other special quality:

Magic Resistance. The helmed horror has advantage on saving throws against spells and other magical effects.

But magic resistance of this kind is only helpful against spells which offer the target a saving throw, which eldritch blast does not - it is a spell attack, resolved against the target's AC. In fact, eldritch blast specifically is quite advantaged compared to many other damaging spells because the damage type that it deals - force damage - is itself a very rare resistance. A search on D&D Beyond at the time of writing shows only three published monsters with immunity (one of which is that pervasive helmed horror again) and none with resistance.

The warlock can also benefit from magical items such as a rod of the pact keeper or wand of the war mage, which grant a bonus to their spell attack rolls and keep their attack bonuses comparable to martial characters using magic weapons, so they are not less likely to be able to hit the AC of high-level enemies than other characters - which is the only other significant factor which might affect eldritch blast's efficacy.

A warlock can expect eldritch blast to be a reliable and useful cantrip at all levels of play, since their attack bonus and damage output will scale with their level and monsters with immunity or resistance to the spell or its damage type are extremely rare.

Answer 3

Eldritch Blast normally

A 17th level Eldritch Blast with +5 CHA and Agonizing Blast about 42 average damage on a full four hits. When faced with an enemy that is immune or resistant to Eldritch Blast, you probably want to compare your other options to this number.

Pick up a weapon and hit them

While it's not your usual mode of combat, any creature with immunity to 5th-level and lower spells is usually not immune to getting brained with weapon. If you choose a Quarterstaff (two-handed) and have 10 STR, your average damage-on-hit will be about 4.5 damage. If you choose a Dagger and have about 16 Dex, your average damage-on-hit will be about 5.5 damage, but you'll hit more often. (These are common stat points for a Warlock at my tables). These options are between 1/9 to 1/7 times as much damage as your Eldritch Blast on full hits.

Sometimes that weapon must be magical and you aren't always privy to one. I'll provide examples of ways to deal with spell immunity together with nonmagic weapon immunity below.

Pact of the Blade

Your pact weapon counts as magical. You may not be very good at hitting, but few things are immune to magic weapons and spells of up to certain levels. You decide which kind of weapon your pact weapon is every time you produce it. If you choose a Greatsword and have 10 STR, your average damage-on-hit will be about 7 damage. If you choose a Rapier and have about 16 Dex, your average damage-on-hit will be about 7.5 damage, but you'll hit more often. Attacking with your pact weapon will therefore be about 1/6 as much damage as your full Eldritch Blast volley, but it's a non-zero contribution when you otherwise would not be contributing. Thirsting Blade would double this contribution per round to about 14-15 damage with all hits for about 1/3 as much damage.

Pact of the Chain

There are no real opportunities exclusive to Pact of the Chain. None of the available familiars have magic natural weapons.

Pact of the Tome

Shillelagh is a cantrip on the Druid spell list that enhances a wooden stick into a 1d8+5 magic weapon. This is about 9.5 damage on a hit which is about between 1/5 and 1/4 as much damage as your Eldritch Blast.

General Options for any Pact

Conjure Fey is a Mystic Arcanum available to Warlocks which allows you to summon a Fey creature, a number of them which deal non-physical damage without casting spells. For example, the Oread deals 18 fire damage on two hits as a non-spell (almost 1/2 as much damage). The Dusk Hag does about 36 psychic damage on two hits as a non-spell (about 85% as much damage). However, at your table, you may not be able to choose what shows up.

Further, you get your Mystic Arcanums of 7th Level and up. Crown of Stars grants you seven attacks worth of 4d12 radiant damage for about 26 average damage on hit which is about 60% as much damage as your Eldritch Blasts. However, this damage is done as a bonus action without concentration so on subsequent turns, you can combine Crown of Stars with any of the other above methods and combine their damage.