Sorcerers got a new metamagic.
You fuse two spells together, combining their energy types. If the next action you use is to Cast a Spell that deals acid, cold, electricity, fire, or sonic damage, select a non-cantrip spell in your spell repertoire that deals a different type of energy damage from that list, and expend an additional spell slot of the same level as this secondary spell. The spell you cast deals additional damage equal to the level of the secondary spell slot expended. The spell's total damage is divided evenly between the energy type of the spell you cast and the energy type of the secondary spell.
The damage increase itself is not impressive... But the energy damage change actually is. And let you target weakness with basically any spell.
Some that I find cool.
Draconic (except poison) and Fire Elemental Sorcerer focus spells, letting you get around immunities with it or target weakness. And let's be honest, breathing fire is cool... but what about breathing fire AND lightning at the same time?
Blistering Invective to give targets persistent sonic damage.
Flaming Sphere, make a ball of Ice and Fire and sustain it each turn.
Acid Storm, a lvl 5 spell that looks weak at first, average 13 damage each turn but have 1 minute duration... what if we it rain another element at the same time? Make it rain fire as well against a white dragon and now each turn it takes +10 to 20 extra damage each turn. If your party have resistance from rings or runes even better, around 7 damage from each element with 5 resistance to both makes the allies only take 4 damage each turn, use the big area.