Dear Dungeon Masters,

I am creating a magical item that will be gifted to my high-level sorcerer. The idea of the item is that it gives them more options to use their metamagic on. I find the list of the currently existing metamagic options a little short.

Do you have any ideas for additional metamagic options? I am not opposed to them being weaker than the existing ones, considering its going to be on a magical item.

Thanks in advance!

Here is a resource for metamagic feats from 3.5e.

I'll be sure to take a look!

Here are a few from around the internet. I have not tested them.

Shifted Spell
When you cast a spell that forces a creature to make a saving throw to resist its effects and has a duration of instantaneous, you can spend 3 Sorcery Points to change the saving throw to another ability score. If the original saving throw uses a physical ability score (Strength, Dexterity, or Constitution), the new saving throw must be chosen from between the other two physical ability scores. Similarly, if the original saving throw uses a mental ability score (Intelligence, Wisdom, or Charisma), the new saving throw must be chosen between the other two mental ability scores.

Widened Spell
When you cast an AOE spell, you can spend  Sorcery Points (1 Sorcery Point for cantrips) to increase each of the area’s dimensions by half, rounded down to the nearest 5 feet.

Accurate Spell
When you make an attack roll for a spell, you can spend 2 sorcery point to get +5 bonus to to the attack roll.

Persistent Spell
When your spell that requires concentration ends early, you can spend 2 sorcery points to have the spell last for one more round, ignoring concentration for that round. The spell cannot last for more than its maximum duration this way.

Shielded Spell
When you cast a spell you can spend 5 Sorcery Points to shield it. A Shileded spell can not be affected  by counter spell.  

Bouncing Spell
When a creature succeeds at a saving throw against a single-target spell you cast, you can spend 2 Sorcery Points for the spell to "bounce" and target another creature of your choice within 30 feet of the original target, without consuming another spell slot.)

Efficient Spell
When you cast a spell of 2nd, 3rd, 4th or 5th level, you can spend 2 Sorcery Point to cast it using a spell slot one level lower than the spell's normal level, without changing the effects of the spell.

Imparted Spell
When you use a spell slot to cast a spell with a range of self, you can spend 1 Sorcery Point to change the spell’s casting range to touch.

Maximized Spell
When you roll damage for a leveled spell, you can spend a number of Sorcery Points equal to twice the spell’s level to deal maximum damage to one target of the spell.

Potent Spell
When one or more creatures would take no damage following a successful saving throw against a spell you cast, you can spend 2 Sorcery Points to deal half the spell’s damage to one of those creatures. The creature suffers no additional effect from the spell.

Precise Spell
When you cast a spell which requires an attack roll, you can spend 2 Sorcery Points to gain advantage on the first attack roll of the spell.

Reactive Spell
As a reaction on another creature’s turn, you can spend 2 Sorcery Points to cast a spell with a casting time of 1 action. That spell’s casting time becomes 1 reaction for this casting.

Reverberating Spell
When you cast a spell with an area of effect and a duration of instantaneous, you can expend Sorcery Points equal to the spell’s level to have the spell (at its lowest level) target the same area at the beginning of your next turn.

I like the idea of sub class specific ones. I have a few I've come up with.

• Chaos (1 sorcery point): Roll a d8 and select a meta magic accordingly if that meta magic cant apply roll again. If on a second roll you still cannot apply that meta magic, roll a wild magic surge.
• Clock work( 2 sorcery points): The roll for the spell is automatically a 10 + mods  either to hit or save
• Shadow (1 sorcery point): When you are in dim light or darkness, you can cast a spell as if it came from another unoccupied  space  you can see that is within 120 feet and also in dim light or darkness. All verbal components and speech that are part of the spell appear to come from that location. 
• Aberrant mind (2 sorcery points): Choose a spell that targets only one creature.  The spells effects are visible only to the target, the damage becomes psychic and any attacks or  saving throws are replaced with an intelligence saving throw.  A target effected by a spell can end the effect early by using an action to investigate the effect in addition to any saving throws they may normally be able to make on their turn. 
• Draconic: When ever you damage a target with dragon's Breath or a breath weapon you can spend sorcery points equal to the spells level to cast a spell, when you cast a spell this way it can only effect creatures who were effected by the breath weapon or dragon's breath. 

I had a thread in the Sorcerer forum earlier in the year collecting ideas: https://www.dndbeyond.com/forums/class-forums/sorcerer/132087-new-metamagic-ideas

Quote from Sisonek >>

Shielded Spell
When you cast a spell you can spend 5 Sorcery Points to shield it. A Shileded spell can not be affected  by counter spell.  

 

This one seems silly when you could just use Subtle for 1 point and give no trigger for a counterspell