Didn't see an old thread to collect ideas for new metamagic options, so figured I'd start one if folks are looking for inspiration for homebrew subclass features or that kind of thing.

I'll start off. Feedback is welcome:

Delayed Spell

When you cast a spell that has an area of effect, you may spend up to 3 sorcery points to delay when it takes effect by that many rounds. You must maintain concentration on the spell while it's being delayed. The spell takes effect when those rounds have elapsed, or immediately upon your concentration being broken.

Echoing Spell

When you cast a spell that deals damage to a single target, you may spend 1 sorcery point to deal 1d8 damage of the same type as the spell to the same target on the next round

Expanded Spell

When you cast a spell that has an area of effect, you may spend sorcery points to add 5 feet to its listed area. The number of sorcery points required is based on the shape of the area. You may not increase a spell's area by more than 5 feet on any one listed measurement:

• line - 1 sorcery point to add 5 feet to its length
• cone - 2 sorcery points to add 5 feet to its width
• cube - 3 sorcery points to add 5 feet to the length of each side
• sphere - 3 sorcery points to add 5 feet to its radius
• cylinder - 1 sorcery point to add 5 feet to its height, or 3 sorcery points to add 5 feet to its radius. You may not increase both

Fortifying Spell

When you cast a spell, you may spend 1 sorcery point to gain temporary hit points equal to 1d4 plus the spell's level

Ricocheting Spell

When you cast a spell that deals damage to a single target, you may spend 1 sorcery point to deal 1d8 damage of the same type as the spell to a different creature of your choice within 5 feet of the target

I like expanded spell the most. Off the top of my head I think I'd add one that lets you change a spell that affects self to be able to affect someone else, I'd have to look into that some to see if it might allow for some unbalanced stuff though.

With echoing, and to a lesser extent richocet, I’d suggest changing the wording to when you hit. So you can’t miss with the spell, and then do damage. Because the way it’s worded now “when you cast,” they can cast their firebolt, miss, and still end up doing damage on their next turn.

Part of me also thinks it should maybe cost a reaction or something. Doing free damage — no attack or save — is pretty big.

Quote from Xalthu >>

With echoing, and to a lesser extent richocet, I’d suggest changing the wording to when you hit. So you can’t miss with the spell, and then do damage. Because the way it’s worded now “when you cast,” they can cast their firebolt, miss, and still end up doing damage on their next turn.

Part of me also thinks it should maybe cost a reaction or something. Doing free damage — no attack or save — is pretty big.

Yeah, when I dashed those out I intended "when you cast a spell that deals damage" to mean you actually dealt damage, not just when you were casting a damage-dealing spell. I was thinking of them as an equivalent to Booming Blade/Green-Flame Blade

I randomly ran into this page which as several nice homebrew metamagics.

https://www.flutesloot.com/sorcerer-metamagic-analysis-5e/#:~:text=Transmuted%20Spell%20is%20meant%20to,cost%20of%20one%20Sorcery%20Point.

Of those examples, I definitely think Expanded Spell has the most potential, and the easiest to balance. The idea of putting a little more "oomph" into a fireball slightly bigger, or a lightning bolt slightly longer etc. is very in keeping with the 5E Sorcerer. I would even let them shrink the area by a similar amount, so you could chuck that fireball into an area where the outer edge would otherwise catch one of your allies. 

For Echoing and Ricocheting, I like the concepts, but I'm leery about auto-damage. For Ricocheting Spell, I would suggest something like "When you cast a spell that makes a spell attack against a single target and hits, you can spend X Sorcery Point(s) to make an additional spell attack against a target within 5' of the original. If that attack hits, you deal Y of the same type of damage against the 2nd target(if the spell deals more than one type of damage, you pick which of them it does). (I use X & Y because I'm not sure what the right balance of Sorcery Point and damage is). And if the spell involves a saving throw vs an attack roll, I would allow it only if the target failed the save, and have the new target make the same kind of save(taking no damage on a success). Maybe I'm being too strict, I dunno. As for Echoing Spell, again I like the idea, but I'm not sure of the right balance for it. If you want to make them easier to pull off, I'd probably want either the point cost raised or the effect limited to use with cantrips or something.

I like these, though I feel like Echoing Spell and Ricocheting Spell may be a bit redundant when we already have Empowered Spell for more damage, and Twinned Spell for more targets (I know the ricochet is automatic but twinning seems better in more cases, and more generally useful).

For Expanded Spell I'd simplify it to just 1 point to extend the length of a line or height of a cylinder, then 2 points to increase the size of a cone, cube or sphere or radius of a cylinder. This should make it a bit simpler and easier to remember (only really need to remember what the 1 pointers are). While some spells may benefit more than others, I think in practice you're going to use this with smaller area spells more, as large area spells are already tricky to use.

I do have one suggestion for another Metamagic:

Expedited Spell

When you cast a spell that has a casting time of 1 minute or longer you may spend a number of Sorcery Points equal to the spell's level in order to reduce its casting time by one order of magnitude as follows:

• 48 hours becomes 24 hours.
• 24 hours becomes 8 hours.
• 8 hours becomes 1 hour.
• 1 hour becomes 10 minutes.
• 1 minute becomes 1 round.

While this is intended mainly for out of combat spells such as more quickly laying a trap with Glyph of Warding, it does allow for a 1 minute spell to be cast quickly in combat which opens up a few power combos (though we don't actually have that many 1 minute spells on the base Sorcerer list), especially when including spells from other sources.

Glyph of Warding is actually the main thing I want this for personally; I always seem to play with frustratingly impatient groups, so they never want to wait an hour for me to set a trap, even though they're the same people who complain about taking too much damage (which traps help to avoid). 🤦‍♂️

i believe distant spell does that already.

Quote from TheTired69 >>

i believe distant spell does that already.

Distant increases the range at which you can pick a target, but it doesn't affect the area the spell covers. A Distant fireball can be targeted at a spot 300 feet away instead of 150, but it still only produces a 20-foot radius blast

This one's probably better suited as a subclass feature, really

Anchored Cast

You may touch an object or willing creature and spend 1 sorcery point to make it your casting anchor point. When you cast a spell afterwards, you may spend sorcery points equal to the level of the spell to have it originate from your anchor point instead of yourself. You lose the anchor point once you have cast one spell through it, you spend 1 sorcery point to create a new anchor point, or you take a short or long rest.

I'm torn on whether the anchor point needs to be within a certain range of you to still work -- on the one hand, casting a spell through it when you're miles away or even on another plane seems wacky, but on the other hand you can't see what's going on around the anchor point without using another spell or ability (most of which already have range limitations), so it's already accounted for somewhat

That's a fun idea!

A range may make sense so long as it's reasonably long (1,000 feet?) and I'd maybe ditch the short rest ending it. I might even go so far as to drop the single-use nature of it since it's costly to cast through; instead maybe have the anchor stop working if it takes damage or is moved too far, and the sorcerer knows if this has happened?

A fantastic idea. I have always been of the mind that sorcerers should have expanded metamagic options, not an expanded spell list. That is a separate discussion that I will not engage in here, but I feel that this will be a wonderful addition for sorcerers at my table. I will keep tabs on this thread.

Delayed spell probably shouldn't require concentration. There's a bunch of stuff already vying for that and having to burn it on NOT setting a spell off is a waste. Plus you can just ready an action to cast as well. HOWEVER, if holding it INCREASED the damage or gave it some extra effect, this would be far more worth-while. Especially if it didn't take up concentration.

Echoing spell seems really weak. 1 Sorc point for 1D8 just isn't a lot. Maybe drop it down to a d6 but make the number dependent on spell level. 

Expanded seems great but you need to both cut the cost (2 instead of 3) and I'd let you stack it. 5 feet on a fireball *might* hit an extra enemy on occasion, but you're better off just placing it better... But 10 feet on the radius? Now we're talking! Heaven forbid you sink 22 points (the max a sorc can naturally have assuming MMA) for an expanded 55 foot radius.

Richocheting seems kinda pointless at 1d8. Why aren't you twinning instead? Early on it's not much difference and later 1d8 just isn't a lot of damage.

Here's my suggestions:

Arcing: Costs 1 Sorc points. If this spell kills a foe, any excess damage will be dealt to all targets within a 10-foot radius divided up evenly. Dex save for half. No special effects.

Overcast: Costs X Sorc point (Cantrip - 3, 1 point. 4, 5, and 6, 2 points. 7, 8, and 9, 3 points) and 1 action. Cast a spell. On your next turn you may actually cast the spell. When you do reroll all damage dice and add half the damage (rounded up) to your original total. You may hold this spell for additional turns so long as you do not cast during said turns to stack this effect. Each turn you do you must pay the point cost again. This cannot be cast out of combat. 

Infused: You may use two meta-magics on this spell. The point cost this spell is increased by 50% (rounded up, min 1).

Mimic: You may cast a spell of level 5 or lower that an ally cast  during their last turn as if you had cast it. The cost of this spell is the same as if you created a spell slot. If the spell had material component with a gold cost, you must have the component or the spell fails. (Don't know if I should add a concentration limit or not). This does not apply to ritual spells.

Ritual: You may cast any ritual spell. The cost is double it's spell level as sorc points.

Arcane unravel: You reach out to grasp the arcane with your innate magical abilities. Make a contested spell roll. On a success you may remove one magical effect within a 60 foot radius. You do not need to see the target for this to work. If this fails no points are spent (though the action is wasted). Costs 3 sorc points.

Feedback: This is used as a reaction and does not count as a spell. When target creature within 60 feet casts a spell that deals damage, they will take half the damage (rounded up) as damage to themselves. Spell save stuff. If they succeed they take half damage (quarter damage total). Cost = the level of the spell divided in half (rounded up).

Arcane Strike: When you cast this spell, it counts as a melee spell attack targeting AC. Use your spell to-hit bonus. No additional effects. Any normal melee damage is dealt as well. Costs 1 SP. Basically allows you to turn a save into a 'normal' attack at the cost of requiring you to be in melee range and losing any additional effects.

Absorption: Costs 3 SP. Cast as a bonus action. When you get struck by a spell you gain half it's level (rounded up) as sorc points. Requires concentration. Can be maintained at a cost of 1 SP per round. 

No clue how balanced these are. Just some ideas off the top of my head.

Edit: I would like to add that there should probably be a bit of a focus on new ways to use sorc points instead of just pure spells; especially if modifications are made to the amount of metamagics you can learn. Because there's only so many ways you can augment a spell.

Here's a few new Metamagics I thought of,  though I'm not sure of the balance

Dampened Spell
        When a creature casts a spell within 60 ft of you, if that spell has an effect that increases when cast with a higher level spell slot, you may use your reaction and spend a number of sorcery points equal to the level of the Spell to apply those scaling effects in reverse. For example, Fireball adds 1d6 fire damage as spell level increases; using this metamagic, a Fireball cast at 3rd level would deal 7d6 damage, and require 3 Sorcery Points to do so. You may apply this metamagic multiple times to the same spell, but you cannot dampen a spell to where it would not affect or damage at least 1 target.

Not sure how useful this might be, as a sort of "soft counterspell', but it might be good for non-damaging effect spells like Charm Person, as they tend to scale better than damaging spells.

    Stocked Spell
        When you use your Action to Ready a spell, if the trigger for your Ready Action has not happened by the start of your next turn you may spend your Bonus Action and 1 Sorcery Point on subsequent turns to keep the spell readied with the same trigger without losing it. You may spend another Sorcery Point at the same time to change the trigger for the Ready Action.

Again, not sure of a super good use for this, but maybe it needs to "charge up" the spell or something at an increased cost.

    Usurped Spell
        If a creature within 60 ft is concentrating on a spell, you may use an Action to attempt to capture the spell. Spend a number of sorcery points equal to twice the spell's level and make a contested spellcasting ability check against the target spellcaster. If successful, the spell becomes sustained by you instead of the original caster. You may choose to change the target of the spell as though you had cast it, though the spell retains whatever duration that has elapsed from the original casting time. If you failed the contest, you regain half of the Sorcery Points used to attempt the contest.

This one I'll admit is weird, and I'm not sure how to balance it with regards to SP cost or effective power, but how fun would it be to be able to steal a spell?

    Supported Spell
        If a friendly creature within 30 ft casts a spell, you may use your reaction to increase the level of the spell cast. You must spend a spell slot and a number of sorcery points equal to the level of the spell originally cast, and the level of the target spell increases by the level of the spell slot you spent.

A sort of combined casting mechanic, allowing you to boost the power of friendly spells, though given how terrible upcasting is, this might not be as useful as I'm hoping.

Dampened Spell
        When a creature casts a spell within 60 ft of you, if that spell has an effect that increases when cast with a higher level spell slot, you may use your reaction and spend a number of sorcery points equal to the level of the Spell to apply those scaling effects in reverse. For example, Fireball adds 1d6 fire damage as spell level increases; using this metamagic, a Fireball cast at 3rd level would deal 7d6 damage, and require 3 Sorcery Points to do so. You may apply this metamagic multiple times to the same spell, but you cannot dampen a spell to where it would not affect or damage at least 1 target..

Dunno how I feel about this. It kinda feels like it teeters between 'overpowered' and 'useless'. Plus, some spells do scale with level that this wouldn't make a lot of sense with (like stone wall). I think the big issue here is, why spend a meta-magic slot for an ability you can just get as a spell (that full-counters no less). Especially since you can swap out counterspell if you need to (for some reason), but not a meta-magic

This sounds useful. Situational, but useful.

  Usurped Spell
        If a creature within 60 ft is concentrating on a spell, you may use an Action to attempt to capture the spell. Spend a number of sorcery points equal to twice the spell's level and make a contested spellcasting ability check against the target spellcaster. If successful, the spell becomes sustained by you instead of the original caster. You may choose to change the target of the spell as though you had cast it, though the spell retains whatever duration that has elapsed from the original casting time. If you failed the contest, you regain half of the Sorcery Points used to attempt the contest.

Interesting. I feel like this could be extremely easily abused. I would be worried about the point scaling (10 points for a level 5), but I can see this being useful.

    Supported Spell
        If a friendly creature within 30 ft casts a spell, you may use your reaction to increase the level of the spell cast. You must spend a spell slot and a number of sorcery points equal to the level of the spell originally cast, and the level of the target spell increases by the level of the spell slot you spent.

My main issue with this one is 'why didn't they just upcast it themselves?' Plus this would allow them to cast beyond their level which... I dunno how I feel about that.

Self sustaining spell. 
when casting a spell repeatedly in the same area and the same target you can make the spell permant after one month of casting, doing this consumes all your sorc points for the month. 

magical interference 

you may spend 3 sorc points and a bonus action to negate a lairs actions for 1d4 rounds. 

The only one I liked was Expand.  Even that needs some work. Here are my comments:

Delayed Spell:  Cost too much for the effect.   I would say 2 points to delay it upto 2 rounds, maintain concentration, but breaking concentrion ends the spell without effect.

Echoing Spell:   Not worth it except at very low levels.   I would let this work for multi-target spells if you pay 2 points, all as one metamagic.

Expanded Spell:  Line sucks.   Make it 2 point to add 5ft to the width, not length.  No one cares about an extra 5 ft on the end.  Cones are supposed to be as wide as they are long, so make it 3 points and add 5 ft to both length and width. Cube and sphere are fine. Cylinder should be 4 points to add the radius (as 5 ft added to a radius = 10 ft to a diameter.

Fortify Spell: Should either be when you cast a healing or necromantic spell only.

Ricocheting Spell is again too weak.  At low levels it seems worthwhile, but not much later.  Perhaps making it "exploding spell" and for 2 points it does 1d6 damage to all within 5 ft.

On a side note:  I would not allow expediated spell to reduce time to cast to less than 1 minute.  Casting time of less than that turns non-combat spells into combat spells, with major potential for abuse.  I see a ton of abuses for Anchored Casting, unless you require concentration from the time you Anchor till you cast the spell. 

Quote from Mog_Dracov >>

Delayed Spell:  Cost too much for the effect.   I would say 2 points to delay it upto 2 rounds, maintain concentration, but breaking concentrion ends the spell without effect.

 

I don't know what you mean by "cost too much for the effect", since the change you proposed is more expensive (2 points for up to 2 rounds, as opposed to 1 point per round delayed) and is even weaker since the spell doesn't even go off if your concentration gets broken

I modeled the original idea after delayed blast fireball -- basically, "if you can delay a fireball, why not a different spell?" I think snowtworf is right though that it would probably have to have some additional boost (as DBF does) to make the delay and point cost worthwhile. It's just tough to figure out what the boost might be if it isn't a spell that involves rolling dice for an effect (i.e. a damage or healing spell, or something like sleep)

Not every spell needs to work with every metamagic effect. Twinned doesn't work with AoE spells for example, and that's just fine.

Quote from Mog_Dracov >>

On a side note:  I would not allow expediated spell to reduce time to cast to less than 1 minute.  Casting time of less than that turns non-combat spells into combat spells, with major potential for abuse.

This isn't really a problem without multiclassing and even then I'm not sure it is. If you look at the 1 minute casting time spells available to sorcerer then there's nothing that can really be abused; you could use creation to block an entry way or something, but it's not especially OP.

The Tasha's Cauldron optional feature to add more spells doesn't add any minute casts.

You'd need to multiclass to gain anything you can really exploit, and even then none of them is that bad given the high cost; for example throwing down symbol as an action could be nasty, but it's costing you a 7th level slot and 7 sorcery points for the privilege. A Divine Soul could cast regenerate as an action but for combat healing heal is better. You could maybe exploit leomund's tiny hut with a bit of effort, but that's true of that spell anyway. You could maybe wreak havoc with mighty fortress but then anyone could do that with a Daern's Instant Fortress if they have one, again there's the cost.

I see the point, but I'm not sure that there's anything that's properly exploitable?