Innate spellcasting x / day: is it x attempts or x successful casts?

Question

The party, which includes a bard and a wizard both with counterspell, will soon be facing a marid. The marid's total time on the battlefield will likely largely depend on whether or not he is able to get off his conjured water elemental to act as a blocker.

The marid has Innate Spellcasting with conjure elemental at 1 / day. I am assuming the " 1 / day" is what the MM refering to in this case when it says (p. 10):

An innate spell can have special rules or restrictions.

The marid's Innate Casts require no material components, but conjure elemental also requires verbal and somatic components, so the casting can still be counterspelled.

The marid plans on leading with fog cloud to either obscure his subsequent casting or draw any initial counterspells, or simply flying out of range, but either way it is still possible that at least one of the resourceful party members will be able to counterspell his conjure elemental. If that happens, does he get another attempt or is he done? Can he keep trying until he is successful?

Does the 1 / day restriction on conjure elemental limit the marid to one attempt, or one successful cast, per day?

The preponderance of opinion on this site is that a countered spell costs the caster the slot, although I find it hard to believe that we don't even have a Sage Advice ruling on that. If your answer to this question depends on whether a countered spell still costs a slot, it probably would be best to make that assumption explicit.

Answer 1

The monster can initiate X castings per day

The Monster Manual gives the following explanation for this notation, in the "Limited Usage" section (p. 11):

X/Day. The notation “X/Day” means a special ability can be used X number of times and that a monster must finish a long rest to regain expended uses. For example, “1/Day” means a special ability can be used once and that the monster must finish a long rest to use it again.

The special ability we're concerned with here is to cast a spell. It does not matter what happens to the spell or how it takes effect. Once the monster uses its special ability to cast the spell, it has used one of the charges for its special ability.

As such, even if the spell is countered, its charge has been depleted, and a long rest will be needed to recover it.

Answer 2

Attempts

Counterspell says “the spell fails”; it doesn’t say “the spell is not cast”.

Answer 3

If we agree with the consensus ruling that Counterspell burns a spell slot when used on a spell cast with a spell slot, the same should apply to other cases of using up a different resource that was powering the spell.

Whether that's charges from an item, a class (e.g. warlock mystic arcanum) / feat / racial ability to cast a spell once per rest without a spell slot, or x/day Innate Spellcasting, it uses up the ability/charge(s) as if you did cast the spell, same as with spell slots.

The Counterspell wording itself doesn't refer to spell slots. That's a specific (but common) case people have asked about and gotten tweet responses from Jeremy Crawford. But nothing in those tweets or any rules wording suggests that the same principle wouldn't apply when the spell is coming from something other than a spell slot. Instead, we can take Crawford's tweets as guidance on how to interpret the phrasing "the creature's spell fails and has no effect" in the general case.

An innate spell can have special rules or restrictions.

Yes, it can, but usually that's in terms of cast time or material components. If it's not mentioned in the statblock, it's not different from normal casting.

If no text spells out a different interaction with Counterspell than usual, there isn't anything special.

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It makes narrative sense: unlike abandoning the casting of a longer-cast-time spell, Counterspell disrupts the magic of the spell after the (mental?) energy has been expended to create the effect, but before the magic can cause its intended effect.

At least that's one narrative explanation. According to Crawford tweets, if you counterspell someone during the casting of a long-cast-time spell, the spell slot is still lost (if it wasn't a ritual); this doesn't quite fit the narrative I suggested, or requires a special explanation for that case. Counterspell's rules doesn't make an exception for interrupting long-cast-time spells before their final round.

If you wanted to rule differently for long-cast-time spells, you could argue that Counterspell does not end the casting of the spell, it only negates its effects. But the spell slot is only expended at the end of the cast time, if you continue spending your action on later rounds to finish pouring energy into the already-disrupted casting.

But long-cast-time spells are getting off topic from Innate Spellcasting and other non-spell-slot powered casting. Those things are orthogonal: counterspell of long-cast-time spells should work the same whether it was powered by a spell slot or some other per-rest or per-day resource.