Disclaimer: Yes, I am aware that I haven't actually played Grendel. However, enough has been shown in order for me to provide this feedback.
DE allowed some content creators (I'm assuming there were several, yet I only saw one) to test him prior to release. He is quite survivable, yet has two major issues: his passive and his third skill.
1. Passive: The more enemies he ingests, the higher the armor value.
The issue: The passive only works on enemies that have been eaten by Grendel. The only way to ingest them is with the use of his first skill. The problem? It's not a passive, it's an aspect of his first ability. Passives cannot solely be triggered by abilities. They have to be able to be triggered through other means. Even with Octavia, her passive can be triggered with the use of Transference.
My suggestions: Move the armor bonus per ingested foe perk to his first skill (since it already is one). Next, his passive could be that, Grendel, being a glutton, can pick up resources and ammo in order to gain health, shields and/or energy. Note, the player still gets the benefits of the drops, they simply will give Grendel some health, shields and/or energy. Additionally, when Grendel dodges, enemies he makes contact with are knocked over because of his bodyweight.
2. Regurgitate: Hurl a vile covered enemy as a toxic projectile.
The issue: An ability that has no use without having first used the first skill. Again, it's not synergy, it's dependence. Again, like his passive, Regurgitate is an aspect of his first. To add insult to injury, Feast can already throw up enemies, dealing Toxin damage. Regurgitate simply does this with higher projectile speed. Groundbreaking. This is EXACTLY why Wisp's original third skill was changed. It had NO use without using Reservoirs first.
My suggestions: Regurgitate is a tap/hold. Tap causes Grendel to vomit a stream of stomach fluids that deals Corrosive and Toxic damage in a cone and is a channeled skill. Should Grendel have enemies ingested, these will ejected out of his mouth by holding the ability key.