Crawlers were 10 times more potent vs other demigods a few patches back, because they could actually swarm all over a target quickly and easily... but GPG nerfed their "agility" and now they are lethargic rolly-pollies when trying to attack onto a moving target. They also nerfed horn of battle. Blood of the Fallen is all around better for Erebus, even doing a nybrid minion build. Horn just doesn't keep minions alive under tower fire, and regen is never as good as not getting killed in a focus fire.
Hybrid builds are all around better now for Erebus if you want to rolly-pollie
1 point in conversion is good enough. Figure 5 minotaurs and 2 archers on each side for creeps most of the game, and that gives you on average 7 crawlers each wave if you can stay near the dying troops on both sides.
1 point in coven is incredibly potent, not so much after that.
You have the following needs to play a strong hybrid rollie pollie... and how to fill them in for the 1st 10 levels depends greatly on what is happening on the game.
2 bat swarm
If you really want to play a minion build... concentrate on steam rolling towers, but don't expect to do well against good players.
I would honestly say bite is your dump skill to go full minion. 1) You cant bite towers and 2) You're not going to have the power to last in a stand up fight putting more then 2 points in minion skills.
Swarm / mist keeps you alive and stun keeps you and your teammates alive.
Your "need" skills to fill in for level 10 become radically different playing a minion build. It is a little easier to manage decisions over a hybrid build though.
1 bite (snare / heal)
After that I'd say fill in conversion and morale, and remember not to engage enemy demigods too much... just keep trying to steam roll as many towers as you can and be all around annoying evasively capping flags using stun and bat swarm.
For favor, you should go with ring of divine might, because 1) You wont have the anti-DG skills to do a stand up fight even if you take blood of the fallen, and 2) that is alot of extra damage inflicted on towers with your 1st point in coven...