Rules clarification

As a DM I believe it is my duty to make sure game follows 5e rules, especially in games I run based on WotC scenarios. I will be explaining my decisions in this thread. I welcome any pointers to game rules or questions/clarifications in this thread.

Let's start with
Chapter 9: Combat -> Actions in combat -> Help action
There is very good reason why 5e designers defined this as a Combat Action: this help only applies to actions that could be done in 6 seconds
There is a different rule describing how PCs could help each other with complex tasks

Chapter 7: Using Ability Scores -> Ability Checks -> Working Together
In this chapter there are two significant limitation
"A character can only provide help if the task is one that he or she could attempt alone
Moreover, a character can help only when two or more individuals working together would actually be productive"

As a rule of thumb I will not allow help with Int and Wis based skills (exception may apply). If you help anyone with Str or Dex checks that results into taking damage you will both be taking the damage.

Does that sound fair?

Rules say:
So if you ever want to announce action of braking anything - you ware welcome to do so, though there may be cases when I narrate you keep trying but with no success. That would mean it is either indestructible your your damage output is too weak.

If common sense say it can be done there are still some mechanics, read more at PHB or basic rules about Objects in "Chapter 15: Running the Game"

For example all objects are immune to poison and psychic damage
And some Solid objects may have Damage Thresholds For example if a wooden door have Threshold of 15 you would never be able to do any damage to if with your dagger, even if you roll a nat 20 damage is max 13 even with dex modifier +5. But a greataxe would do the job eventually, though you would spend some time because you rolling 15 damage in a single hit requires some luck. If you have enough time I would not even ask you to roll anything

inspiration
If you have inspiration, you can expend it when you make an attack roll, saving throw, or ability check. Spending your inspiration gives you advantage on that roll.

Please note that you need to decide and use inspiration before you roll a D20. You can't re-roll. It is a one time advantage, not a re-roll.

When rules are ambiguous I'll be checking official game designer advice sage advice compendium
If no answer in advice I will rule as better for players. I'm afraid though this
Since Elemental Cleavor say it infuse weapon itself I lean to say that you can certainly reroll 1 and 2 for EC

Not so sure about Superior dice (i.e. Menacing) ... it does not explain reason for extra damage. Is it a weapon or the Menacing you perform? If I'm not sure I'll allow player to chose

But Strike of the Giants (i.e. Cloud Strike.) directly say "imbue the attack" not the weapon. No reroll here.

Note that all you can do is "one melee attack" (unless you have war caster feat and can cast a spell instead).
You can't draw a weapon as part of your Opportunity Attack, if you have no weapon in your hand you can do unarmed strike instead. Note: since Opportunity Attacks is a reaction it interrupts current creature turn and that turn could be changed based on result of a reaction. Creature could decide to stop moving for example or it could be forced to not move if you have sentinel feat.

Dispel magic clarification
Whenever a detect magic shows an object has a magic aura you can choose that object and cast dispel magic on it. There will be cases when I explain detect magic detects presence of a magic but you don't see any object that would give the aura - in that case you wouldn't be able to dispel it (i.e. if a magic object is under the pressure plate, behind the doors, etc.)

If you want to dispel an object pick an object and "make an ability check using your spellcasting ability".

Warning: dispelling a magic will stop that magic from doing what it does. i.e. if there is a magic trap that is preventing poisonous gas to be released until you touch something - dispelling the magic will automatically release the gas. So don't get mad at me IF dispel magic will do more harm that good and remember - Acererak who created all of the traps in this place for you are is experienced in doing that and have been improving his traps based on how other adventurers have been trying to break them.

make an ability check using your spellcasting ability.

Means you roll 1d20 and add wisdom/charisma or intelligence modifier. You do not add proficiency bonus

I can't explain it better than here
Short answer: No, you don't benefit of Recklessly throwing stuff.

Since you getting some magical items I'd like to clarify:
PHB Chapter 14 has paragraph on Using a Magic Item. I will not repeat it just summarize:
1. Either identify spell or short rest focusing on one item is enough to learn it's properties. Casting identify provide additional info such as how many charges it has, if any and whether any spells are affecting the item
2. If item has "requires attunement" property the same short rest mentioned above would be enough to both learn properties and attune

Conclusion: if item requires attunement the only benefit of casting identify is to learn how much charges it has. If it requires no attunement identify will allow you save 50 in-game minutes

In my game all cases of perception checks (traps, hidden creatures, etc.) work following - when player announce action that DM believe may lead to trap discovery, hearing some voices, etc. DM will consult with PC passive perception first and ask to roll ability check if passive perception is not enough. If player have already rolled - it will save time. If player rolled perception, but DM don't believe PC actions could lead to a discovery, DM will ignore the roll.

There is an exception to the above rule. If player what his PC to check wall for the hidden doors (which as we established is extra hard to achieve) player need to choose 5 feel wide wall segment and roll perception check. Player could repeat that roll for either same or other segment as much time as he desire, but DM will increase DC for discovering doors every time player rolls a dice regardless of the result. A long rest and a secret door discovery resets the penalty to 0.

Just to help us understand each other better. My understanding is following:
I can narrate character investigate an event, a problem or statement.
If player announce he is investigating an object ... well let me explain how I understand thatNow, let's see what just happened in game: objects PC investigating are the chests. She already know what they are made of but anything apart from that is a mystery by the design

If investigation would be done on the objects inside the onyx chest I would - based on good roll - tell that Tinkara could conclude the things belonged to a wizard who's body has been either disintegrated or consumed, leaving dress and equipment.

Spell Freedom of Movement clarification
While spell say "target's movement is unaffected" it does not say spell prevent target from force movement.
In a combat (or combat-like) situation it means for example:
1. Enemy could grapple target and move on their turn, target will need to spend 5 feet of movement to automatically escape grappled." - this is explicitly stated in spell description

2. Freedom of Movement does not make you immune to shove or prone. It does not prevent you from being pushed away by any creature feature or any spell

3. Freedom of Movement will not prevent you from falling off the mount when you would otherwise do so

Question: can I ready attack outside combat?

Answer (short): no

Answer (mechanical):
5e has strict rules on how to organize combat:
1. Determine surprise. 2. Establish positions 3. Roll initiative 3. Take turns. ...
Only as par of step 3 you can do "Ready action on your turn, which lets you act using your reaction before the start of your next turn....

Answer (logical):
When both you and your enemy are anticipating a combat and want to attack each other as soon as possible (i.e. both parties "ready an attack") and the trigger to attack it the same it is the dexterity check that will decide who acts first: that's what initiative roll is about.
i.e. you are on two different sides of a crystal wall and see each other and that crystal is about to collapse. Who swings their sword first, when that happens? Not the the player who is most vocal, but the character who rolls better initiative.

Corner case:
In current game situation you are ready to slash your sword when see something to slash at, right? And you will only see that when the creature in the water try to constrict you. That would be strange if we roll initiative, you win and can slash at the creature that did not attack you yet... so I decided to not go with surprise round, but simple automatic fail on dexterity check (initiative roll). That's not per rules, but that's how ruled.