Who decides what PHB variants are in play?

The rules variants presented in the DMG are clearly there for the DM to decide upon.

SOME of the variants in the PHB say that they are the DM’s prerogative. For example, VARIANT: CUSTOMIZING ABILITY SCORES (PHB p.13) says "At your Dungeon Master’s option, you can use this variant for determining your ability scores."

However, the VARIANT: ENCUMBRANCE (PHB 176) says "Here is a variant if you are looking for more detailed rules for determining how a character is hindered by the weight of equipment." AFAICT, there is no discussion of encumbrance in the DMG.

Does this mean that, RAW, individual players each decide whether or not they are using the encumbrance rule, and that a given game might have some players using the variant rule and others not?

(I realize that by Rule 0, A DM could decide that the variant rule was in play or not)

How does the UA Revised Ranger’s “Greater Favored Enemy” interact with “Favored Foe” from the UA Class Feature Variants?

If a Revised Ranger chooses to use the Favored Foe variant from the most recent Unearthed Arcana, they replace their original Favored Enemy feature. How does this interact with their existing Greater Favored Enemy feature?

Even when the Ranger doesn’t have access to Favored Enemy, do the benefits it provides still apply to the Greater Favored Enemy?

Favored Enemy (original)

Beginning at 1st level, you have significant experience studying, tracking, hunting, and even talking to a certain type of enemy commonly encountered in the wilds. Choose a type of favored enemy: beasts, fey, humanoids, monstrosities, or undead. You gain a +2 bonus to damage rolls with weapon attacks against creatures of the chosen type. Additionally, you have advantage on Wisdom (Survival) checks to track your favored enemies, as well as on Intelligence checks to recall information about them. When you gain this feature, you also learn one language of your choice, typically one spoken by your favored enemy or creatures associated with it. However, you are free to pick any language you wish to learn.

Favored Foe (variant)

You can call on your bond with nature to mark a creature as your favored enemy for a time: you know the hunter’s mark spell, and Wisdom is your spellcasting ability for it. You can use it a certain number of times without expending a spell slot and without requiring concentration a number of times equal to your Wisdom modifier (a minimum of once). You regain allexpended uses when you finish a long rest. When you gain the Spellcasting feature at 2ndlevel, hunter’s mark doesn’t count against the number of ranger spells you know.

Greater Favored Enemy (original)

At 6th level, you are ready to hunt even deadlier game. Choose a type of greater favored enemy: aberrations, celestials, constructs, dragons, elementals, fiends, or giants. You gain all the benefits against this chosen enemy that you normally gain against your favored enemy, including an additional language. Your bonus to damage rolls against all your favored enemies increases to +4. Additionally, you have advantage on saving throws against the spells and abilities used by a greater favored enemy.

(emphasis is mine)

Would it be possible to get a dragon to CR27 using only official material and variants (Shadow Dragon/Dracolich, innate spellcasting, etc.)? [on hold]

Ancient Gold Dragons and Ancient Red Dragons have a CR of 24. This means that, if you were to have such a dragon of the innate spellcasting dragons variety (MM p.86), they could know spells up to 8th level. I’m wondering if it would be possible to get a dragon up to CR27 (to give it access to 9th-level spells) using only official materials and variant rules.

By my calculations, an Ancient Gold Dragon has a defensive CR of 25 and an offensive CR of either 22 or 23, giving it an average CR of 24. In order to get it up to an average CR of 27, the easiest route would most likely be by raising its OCR, as it has more room for improvement. In order to get it to CR27, its OCR would need to be at least 28. The Ancient Gold Dragon gets a +2 boost to its OCR due to having an exceptionally high attack bonus, meaning its damage output would need to be equivalent to CR26, which is 231-248 damage per round on average over the first three rounds of combat.

As far as I know, making the dragon a Shadow Dragon or Dracolich doesn’t significantly increase its damage output. A Shadow Dragon’s breath weapon is more lethal due to instantly killing upon dropping a character to 0, but I don’t know how to quantify that.

Is there a selection of spells of levels 1-8 that could be given to a dragon in order to get its OCR up to 28? Or is there another way to get a dragon to CR27 that I’m overlooking?

Bloodline Mutation Variants & Transmutation

Looking at the Sorcerer Bloodline Mutation Variants from Paizo’s Magic Tactics Toolbox. Do either of the three variants (Havoc, Intensity, or Piercing) have any effect while ‘you’ are under the effects of a transmutation/polymorph spell?

Are there any other Mutations (or similar variants) that have been published that would affect being polymorph as such?

Are “extended” variants of a spell considered a separate spell for the purpose of purchase?

Are “extended” versions of spells considered separate items for the purpose of purchasing spells?

For example the spell “Detect enemies” has a variant “Detect enemies, extended”, if I were to purchase “Detect enemies”, do I also get “Detect enemies, extended” for the same cost or must I purchase “Detect enemies, extended” separately?

How can I remove “As low as” in Magento 2.3.1, if all the prices of the variants are the same?

How can I remove “As low as” if all the prices of the variants of the configurable product are the same? It doesn´t make sense to me to show “As low as” when all the colors and sizes are equally expensive. I have some products that have different prices for the sizes, so they are absolutely correct with the addition “As low as”. Simply the ability to disable it at all with display:none is not my goal. Help really appreciated!