erebus nightwalkers counter?

Don't pick Sedna. She's a melee Demigod that doesn't have AoE. It's like asking the question "What are the Rook counters to Regulus?"

I can't foresee my opponents in Pantheon, but thanks for your input.

parasite egg. mines.

The counter to minions is just getting your own minions (ofc no yetis) and distracting his minions with your own, even if his are many times stronger there attacks will be scattered and wont burst you down, this gives you time to kill the General. Also remeber ARMOR, a few pieces of armor will make you largel invincible againt minions.

Night Walkers are really quite friendly, if you just let them be for a little while, they will happily take you over to the dark-side.

Reg needs to hit them with mines, then you need to silence so they can't mist while you hit them with everything you have.\

As a Sed you need to take Silence, pounce, and heal. Expect to be bitten so don't speed stack at all: you're unlikely to be chasing them down.

definitely on the wrong side of the rock>scissors>paper on this one. not alot you can do.

best bet is to focus attack one of the Erebus' and try to knock him out early. you'll have to Tank for the team while Regulus focuses on bursting them down with Mines and MotB. not sure an AA Reg can really get the job done. at the point in the game you got to, with the specs you chose, it might have already been too late. 

Yeah, I know my comment wasn't what you were looking for, but there's not a whole lot that can be done. It's a bad Pantheon matchup (go figure ;)).

Next time I encountered Erebus swarm, I started a minion build, which helped, but it made me remarkably squishy.  Also, the mess of minions made it difficult to target heals.  But it did seem slightly better than before.

In a 2vs2 against two minion builds you've already lost Conquest and Fortress with a Sedna hogging a DG slot, unless the Erebi are idiots.