The sister feat to Telekinetic, above, the Telepathic feat gives you the ability to speak to other creatures with your mind. Your powers of telepathy allow you to communicate in a language you know, and to read their thoughts. Great for communicating secrets silently with your party members in tense scenarios—or for spooking patrolling guards and learning your foes’ deepest secrets! These are optional rules. As it says at the beginning of Chapter 1, one of the options featured in the chapter is (p. 7; emphasis mine): The fey theme continues at Level 7, where you gain advantage against being charmed or frightened. Eventually you learn to cast misty step almost at will and you can summon fey to do your bidding. Ranger – Swarmkeeper

Akin to the Fey Touched feat mentioned earlier, a character might gain the Shadow Touched feat from being lost in the drab and ghastly landscape of the Shadowfell. In addition to improving one of your ability scores, you also gain the ability to cast invisibility, as well as another shadowy spell. Skill Expert

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The College of Creation centers on the “Song of Creation,” the primeval harmonies that pre-exist the known world. These bards draw on this song using art, music, and poetry. If your table is in between, or has a mix of different playstyles from different players, consider how imposing or relaxing the subclass feature level requirement will affect the fun of both the specific player involved, and the rest of the table. You have been exposed to raw power from the Feywild, a plane of powerful and tempestuous emotions. This feat represents your connection to the capricious power of the fey by granting you a small bonus to one of your ability scores and the ability to cast misty step and another spell from a particularly fey list. These are not rules. These are suggestions to help a DM facilitate a subclass change, which is a pretty significant change. The idea here is to make the transition just as meaningful as where you came from and where you're going. How would I personally work a subclass change?

I present rogues as a use case for why I would break from the guidance given in the book. Rogue subclasses have a huge gap in features. Once a rogue gets their first subclass features at 3rd level, they don't get another until 9th level. Nothing in Crusher, Piercer, or Slasher says the damage has to be melee. I mean. Piercer would even work with the Ice Knife spell!The other stand out for me is Piercer;any DEX-build martial with a Shortbow or Longbow and a Spear or Rapier gets a pretty significant damage boost. I can see Rangers or Kensei Monks especially getting alot of benefitout of this with their other bonuses ( Hunter's Mark or Swift Quiver for the Ranger, Kensei features and Ki-fuelled strike for the Kensei). The second scenario is when I would use the "Sudden Change" guidance. If we are nearing a level up, and my player says "I want to change subclasses", I don't have time to work in significant plot build-up to the change, so I will opt for something like is suggested in this section at the next level up. This interesting archetype is based on the concept of a barbarian that is infused with the power of wild magic. Due to the barbarian’s rage, their emotional state makes them susceptible to the forces of natural magic. As with the Psi Warrior, the Rune Knight is another highly anticipated part of Tasha’s Cauldron of Everything. This subclass can create magical runes that enhance their gear. You gain in number runes you know by your fighter level up to a maximum of 5. These runes allow you to essentially enchant mundane items. The benefits of these runes vary, with many buffs to sight and saving throws. Feats and multiclassing are both optional rules presented in the Player’s Handbook that allow a player to give their character gain powers normally inaccessible to their class, and to give their character narrative depth and nuance through new mechanics. Some gaming groups use both optional rules for maximum customizability, while other groups allow one, the other, or neither, to keep their game simpler or more focused.

at level 7, the swarm can lift you up to give you a flying speed of 10 feet for one minute. As you level, the swarm’s ability to do damage and move creatures grows as well. At level 15 you can become one with the swarm, allowing your to give yourself resistance to damage after you’ve already been hit. Rogue – Phantom On the other hand, if you have a table of "Storytellers", a change at any time is fine, as long as it connects to the character and plot arcs you are creating. Allowing the change to coincide with an important dramatic event can even reinforce the player's connection to their character concept. In this case, you are likely using "Story-based advancement" (DMG 261) anyway, so the events that justify their "Sudden change" are also likely to be level breaks as well - although you can safely ignore whether or not the new level comes with a subclass feature. Phantom rogues become so comfortable walking the line between life and death they nearly become ghosts themselves. The knowledge they gain from the dead is useful in a variety of ways. You also gain the use of psychic blades; essentially soul-powered daggers that can be thrown or used as finesse weapons. As you level these blades grow in power, and you gain other options like invisibility. Sorcerer – Aberrant Mind You’ve undergone rigorous martial training in your downtime, though not enough to become a full-fledged fighter. Instead, you’ve learned how to fight with a particular weapon, allowing you to gain a Fighting Style from the fighter class. Don’t forget that there are a handful of brand-new Fighting Styles in Tasha’s Cauldron of Everything including options for fighting bare-handed, fighting blind, and fighting with thrown weapons. GunnerThe impact of permitting a subclass change at any point in time compared to one allowed at certain levels only largely depends on your play style. You may want to review "Know your players" (DMG 6). At one extreme would be if you had a table of "Optimizers", who "welcome any opportunity to demonstrate their characters' superiority." In this case, I would strongly recommend that you keep to a hard requirement of changing subclass only at subclass-defining level breaks, and that you impose the time and gold requirement of "Training time" as well (although not the quest). Anything less will invite these players to switch subclass solely for the mechanical advantages involved, and you will have things like them reasoning, "Now that I have magic item x or spell y, I get better synergy with subclass z, so I want to switch now." Granting a subclass change to one of them while disallowing it to another one is also likely to generate hard feelings.