Sadly there is no counter for Minion Erebus yet. A good Minion Erebus will always kill you first in a 1vs1 battle or be able to escape in a 1vs2 situation, quickly regaining his full army.
Then you simply haven't asked the right people
Minion LE is fairly easy to counter, actually, it simply requires a little more forethought than when fighting against pure Assassin build LE and an understanding that the build is designed around the concept of segmented DPS so no matter how good you are, it's simply harder to kill a Minion LE than an Assassin LE by design. The trade off it's a lot easier to gimp him because you can kill
his DPS! I play Minion LE and Tower/Boulder/Slam Rook as my favourites, so I'd like to weigh in on counters to Minion LEs.
First, accept that there is no one thing you can do - besides stacking armour - to make this easier. It's simply a tough build. If you're aiming to purely counter a Minion LE, and most LE's I see on the field are Minon LEs, you need make sure you have access to AoE damage abilities. UB Ooze it's pretty good, while Ice TB is easily the best. Make sure you never engage them amongst creep waves - doesn't matter how hard you hit, they'll be respawning their minions and wearing you down the entire time, so pull them back to your Towers or get them out in the open and hit 'em hard - if they're smart they'll run like crazy, because you've just taken out a significant piece of the DPS.
Always grab DMG Upgrade one for your Towers, as the added AoE damage it gives the Towers really helps - even at level one - bring down minion swarms. Also keep in mind that most of the DPS from Minions isn't generated through the minions' DPS, but through Bite's Debuffs + Minions. Stacking armour will mitigate quite a lot of DPS from Minions, and it helps in the early stages when Erebus is relying mostly on himself for DPS. Once he reaches Max NS numbers, he'll most likely begin sending them after you on their own when he or you is retreating, as they'll be quite strong - this is where you tuck tail, hoof it back to your Towers double time - and this is why the DMG Upgrade is important - or Teleport out.
Armour stacking leaves you open to ability damage, so be prepared for 2v1 encounters - pull back the moment you're outnumbered as you simply won't have the sustainability. I recommend the 50gold Totem as it increases your sight range enough to make getting away easier as you can see your opponent coming sooner.
The last thing I can recommend is simply being careful - Minion LEs are weak without their minions, and excell at pester tactics like a Spit UB, so you need to remove their minions first unless you outnumber him - then simply unload on the Minion LE and bring him down ASAP.