Can you (continue to) concentrate on a spell that never had any of its effects take hold?

I have previously asked the following question:

  • Is there any reason to concentrate on the Thunderous Smite spell after using its effects?

And my current question is inspired by that and the following recent question:

  • If I want to affect a creature with a concentration spell and it succeeds its save, do I notice my concentration failing?

I realize that in my previous question I just assumed that you could continue to concentrate on the thunderous smite spell after using its effects, but nobody contested this assumption in the answers, so now I’m asking about a similar, but somewhat different case.

I now ask whether you can (continue to) concentrate on a spell where all of its immediate effects never actually occur. An example of such a spell is bane which has a duration of Concentration 1 Minute and states:

Up to three creatures of your choice that you can see within range must make Charisma saving throws. Whenever a target that fails this saving throw makes an attack roll or a saving throw before the spell ends, the target must roll a d4 and subtract the number rolled from the attack roll or saving throw […]

But what happens if none of the targets fail their saving throw? Can you continue to concentrate on the spell even in this case?

What is the best 2nd level spell to concentrate on to maximize damage?

In a party full of crowd control, the Magus wishes to dish out as much damage as possible. What concentration spell will allow them to do that, under the given circumstance:

  • The Magus is 4th level, any race, any class/multiclass, feats available
  • The damage is dealt out over 1 minute maximum
  • The rest of the party is focused on their own goals, so any preparation or buffs on the Magus will have to come from themselves: (no time limit)
  • Assume things go perfectly 100% of the time: ie enemies will always fail on saving throws, the Magus will always succeed on an attack roll, disregard advantage and disadvantage
  • The only source of damage tracked comes from the Magus’ concentration spell; no need to worry about ensuring their action is free every round to cast another damaging spell
  • Assume all damage is average: 1d6 = 3.5 damage, don’t round
  • If a spell can hit multiple targets, there are 2 available each round
  • These 2 enemies behave optimally for your damage: if an enemy must end its turn in the spells area to take its damage, then 2 enemies in a round will do so.

Do the Illusionist’s Bracers allow you to concentrate on two cantrips?

Illusionist’s Bracers (GGR p178) Says:

whenever you cast a cantrip, you can use a bonus action on the same turn to cast that cantrip a second time.

However some spells like Create bonfire require concentration.
Under spell duration, the players handbook says:

You lose Concentration on a spell if you cast another spell that requires Concentration. You can’t concentrate on two Spells at once.

Do the bracers allow you to concentrate on two cantrips at once?

Can your familiar use the frozen spell bead from Arcane Abeyance to indirectly let you concentrate on a 2nd spell?

Arcane Abeyance (p184 EGtW)Says:

…A creature holding the bead can use its action to release the spell within, whereupon the bead disappears. The spell uses your spell attack bonus and save DC, and the spell treats the creature who released it as the caster for all other purposes.

Find Familiar (p240 PHB) Says:

…In combat, it rolls its own initiative and acts on its own turn. A familiar can’t attack, but it can take other actions as normal.

Can a familiar accept the frozen spell bead and then use it to cast a spell, if so does the familiar concentrate on the spell instead of the original caster?

Can you concentrate on non-spell abilities while raging?

There are a few class features in the game that require concentration, but are not spells : A Trickery Cleric’s Invoke Duplicity, a Glamour Bard’s Mantle of Command, and a Graviturgist Wizard’s Adjust Density. They are all phrased in a similar way concerning concentration :

for 1 minute, or until you lose your concentration (as if you were concentrating on a spell).

Going into a rage stops you from keeping concentration on a spell :

If you are able to cast spells, you can’t cast them or concentrate on them while raging.

But, if a multiclassed character (with one of the above subclasses, plus barbarian) uses such a concentration-based feature then goes into a rage, does that concentration break ? Example : Timmy the Trickery Cleric / Barbarian, Invoking a Duplicity, then raging.

If I cast True Polymorph on my simulacrum and concentrate for the full duration, will casting Simulacrum again still destroy it?

Simulacrum states:

If you cast this spell again, any currently active duplicates you created with this spell are instantly destroyed.

Does this mean that if I take my simulacrum and permanently transform it using true polymorph into, say, a dragon, that if I cast simulacrum again, it would still instantly destroy that dragon I just produced?

If you cast Polymorph on yourself, can you continue to concentrate after if the new form has a very low intelligence? [duplicate]

If you cast Polymorph on yourself to turn into a creature with low intelligence, can you/it continue to concentrate and thus remain in the polymorphed state for the duration of the spell? Or would the spell fail almost instantly because the new creature wouldn’t be able to concentrate?

The question arose from one of our players wanting to cast Polymorph on himself to turn himself into a Black Pudding (MM p.241). We all looked into the distance pensively.

The spell says it can transform to be a beast, so the “Black Pudding” would be out of the question, but some beasts have an Intelligence of 1, like the Black Pudding, for instance: a Lizard.

This spell transforms a creature that you can see within range into a new form. […] The transformation lasts for the duration, or until the target drops to 0 hit points or dies. The new form can be any beast whose challenge rating is equal to or less than the target’s (or the target’s level, if it doesn’t have a challenge rating). The target’s game statistics, including mental ability scores, are replaced by the statistics o f the chosen beast. It retains its alignment and personality. […] The creature is limited in the actions it can perform by the nature of its new form, and it can’t speak, cast spells, or take any other action that requires hands or speech.

(PHB p.266)

Does a duergar NPC need to concentrate to maintain its Enlarge ability?

In the MM page 122, nothing is mentioned about needing to maintain concentration, and there is no wording to indicate a duergar’s Enlarge ability is a spell.

This is in contrast to the duergar’s Invisibility action that explicitly says it must maintain concentration.

So, my interpretation is that this is some sort of innate magical ability, not a spell, and thus wouldn’t require concentration. Is this about right, or am I missing something?