Hmm... Did I mention the details of combo here?
Basically feat wise you're looking at Snowcast, Frozen Magic, Cold Spell Specialization, Draconic Aura(energy:cold), Blistering Spell, Energy Substitution(acid), Energy Substitution(electricity), Energy Admixture(electricity), Empower Spell, and really any other useful Metamagic Feat. That's 9 total plus extras, 7 base, 2 flaw, 1 for selling your soul, 1 for metamagic storm, plus any extras from PrCs so plenty of room.
Pick a fire spell and apply Blistering Spell to it.
Apply Energy Substitution(acid) after that. The spell's descriptor changes to [Acid] and the damage it deals is Acid based.
Note, Blistering Spell is a Metamagic feat dealing damage, Energy Sub can't apply to it.
Now apply Energy Admixture(electricity), the spell is now [Acid, Electricity] and deals both Acid and Electricity damage.
Finally, add Snowcasting. That feat adds [Cold] to the descriptor but doesn't alter the damage types and such.
Icemail Armor and Draconic Aura only checks the descriptor. Up to +6 to the Save DC is obtained.
Cold Snap (a spell) & Cold Spell Specialization only checks the descriptor. Up to +3 per die is obtained.
Caustic Mire desires an effect that deals fire damage, through Blistering Spell your spell does. +1 per die.
Acid Sheath like the cold stuff only desires a descriptor, +1 per die.
It actually deals electricity damage so Stormcaster's Thunderbolt applies. +X sonic damage & save vs stun.
In total, you can be looking at up to +8 damage per die, +1 sonic per spell level, +2 fire per spell level, +6 to Save DCs, and has save vs stun. After Empower, thats 17.25 damage per CL with Fireball with an additional 9 damage.
In other words, I hit you with a Acid, Cold, Electricity, Fire, & Sonic and you are stunned at how awesome it is. Most of it is honestly Feat based really, Stormcaster adds the Sonic and save or suck, but it really is mostly Feat powered.