I can't beat a good Ermac... ****in' Ermac man.
The secret to Ermac is actually pretty difficult to explain.
Ermac has probably one of the most dangerous specials in the game, and because of this you feel afraid to let go of block thus giving him free pressure. And those who say he can't mix up he can. He grabs. has a Low F+4 that sets up for more pressure when it hits. and he has up+4, to break duck blockers(i usually grab anyways though, but they can break it which means sometimes they need to use up+4)
What you need to do if he's special happy is just block then dash in with your offense. Don't ever jump when your midscreen or farther he can force push you on reaction. unless your jumping over his projectile.
When he does his lift and your full screen. DONT EVER jump. It's better you take the ground unblockable damage than to eat his teleport punch. And most Ermacs are greedy for that combo damage. So think of it like this
Ground unblockable damage what... I don't know the % but i'm sure it's roughly 10%.
vs taking 30%+ from Ermac if you jump.
On the flip side.
If you stand there and dash a bit to proc it(Scare him into thinking your jumping with movement.) Stand there and block. You only take 10% for this option, but if he chose to teleport punch. You get a full combo yourself 30%+
So standing there blocking is WAY more safe.
when it comes to seeing Ermac charge his unblockable. I would try to immediately jump. It's a mix up but eating the full charge is worse than eating a early weak version. He has to let go of his unchargable if he thinks you're going to react early. so if he starts reacting early to your drop of your block. You can start Holding block longer and he'l probably leg go of it too early to get the Block breaker attribute (he has to charge it to get it to that level)
When your testing the grounds of your opponent and knowing his mind, you need to explore the safer optoins before exploiting his patterns/weaknesses.
If he's using the fear of his specials to pressure you for free. you need to use movement to make him whiff. Dash block and move around back and forth to bait his special. If he doesn't special and lets say you dash block BACK wards. He will whiff (depending on your spacing) and then you can counter attack. He'd be really stupid to go for a special attack while your dash blocking around as there's a high chance he will hit you while you're blocking. and give you free offense.
If you're having problems elsewhere with ermac I can help you out.
