Does Arms of Hadar hit the caster?

The text is unclear to me.

Tendrils of dark energy erupt from you and batter all creatures within 10 feet of you.

I assume I’m a creature within 10 feet of me, so am I also a target of this spell? Some other spells say "all other creatures", and since this does not it feels like it would make sense to include the caster. But on the other hand, if this spell always damages the caster it seems like it would say something explicitly about that.

So, if I cast Arms of Hadar, do I have to make the save?

Does the Ritual Caster Feat grant access to Subclass Spells?

Ritual Caster states:

You have learned a number of spells that you can cast as rituals. These spells are written in a ritual book, which you must have in hand while casting one of them. When you choose this feat, you acquire a ritual book holding two 1st-level spells of your choice. Choose one of the following classes: bard, cleric, druid, sorcerer, warlock, or wizard. You must choose your spells from that class’s spell list, and the spells you choose must have the ritual tag. The class you choose also determines your spellcasting ability for these spells: Charisma for bard, sorcerer, or warlock; Wisdom for cleric or druid; or Intelligence for wizard.

Would a character be able to chose Druid and gain access to the added rituals from the Druid Subclass Grassland Circle (i.e. Divination)?

Do spells with a range of “Self” target the caster?

New to D&D, and thought about creating a Beast Master. I was wondering if spells with a range of “Self” would count you as the “target” of the spell. There’s some debate in my group, as unlike something such as Cure Wounds, which specifies “A creature you touch,” there’s technically no mention of a target in a Self range spell within the description. A fair amount of people in my playgroup come from a TCG background, where the presence (or lack thereof) of keywords like “target” are essential for determining interaction.

tl;dr Would Paladin Smites or Thunderwave count as “targeting” yourself, and therefore be affected by Beast Master’s Share Spell?

War caster feat and green flame blade, is it legit?

The War Caster feat allows a single-target spell (“must target only that creature”) to be cast instead of a melee strike for an opportunity attack.

Green-Flame Blade appears to have a single target, and then some damage “leaps” onto a creature 5 feet away. The other creature is never referred to as the target, or even “a target”.

I’m pretty sure this is solid from the RAW perspective. Is this legit from a RAI perspective?

Calculating caster level when stacking metamagic feats for spell like abilities

Level 6 warlock is able to maximize as well as empower their eldritch blast in separate rounds. If a warlock wanted to stack empower and maximize in single round, how would you calculate required caster level. Also, what would be the earliest level a warlock can cast empowered-maximized eldritch blast in a single round?

When using the War Caster feat and an Echo Knight Fighter’s Manifest Echo where does the spell originate from?

Inspired by the following question:

  • Can an Echo Knight with the War Caster feat use cantrips for opportunity attacks made by their Echo?

The Echo Knight’s Manifest Echo feature states (emphasis mine):

[…] When a creature that you can see within 5 feet of your echo moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the echo’s space. […]

And the War Caster feat states (emphasis mine):

[…] When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. […]

I am aware that the spell cast using War Caster does not count as an Opportunity Attack. And this makes me unsure what happens when a creature provokes an Opportunity Attack from the Echo and the Fighter chooses to use War Caster.

Is the spell cast from the Echo’s space because the Opportunity Attack would have been made from that space?
Is the spell cast from the Fighter’s space because the Maifest Echo feature only allows Opportunity Attacks to be made from the Echo’s space and not spells?
Is something else the case?

Can an Echo Knight with the War Caster feat use cantrips for opportunity attacks made by their Echo?

The Echo Knight has the following ability:

When a creature that you can see within 5 feet of your echo moves at least 5 feet away from it, you can use your reaction to make an opportunity attack against that creature as if you were in the echo’s space.

The Warcaster feat has the following benefit (emphasis mine):

When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack.

If an Echo Knight has the War Caster feat and knows a cantrip like, say, Booming Blade, can they use the cantrip for opportunity attacks made from the position of the Echo?

Can high level Eldritch blast be used with War Caster?

The final test of the Warcaster Feat is the following

The spell must have a casting time of 1 action and must target only one creature. (PHB 170)

The question I have is whether a spell like Eldritch Blast at character level 5+ qualifies if all of the instances are directed at a single target.

Basically, is the must a restriction on the targeting of the spell, or the selection of the spell itself?