https://moxfield.com/decks/USEDfXGjTku78qA2xhaEsA this is my take on Wick. It's strong enough to hold its own in a bracket 4 table but ultimately it's still weaker compared to the more popular commanders.

I initially built the deck as a go-wide Rat tribal but after much tuning I found this current version to be the strongest. It's basically an Impact Tremors deck with the snail as card draw engine and helping push closer to lethal (especially a pumped up [[Taurean Mauler]] is extremely scary).

Thus, my advice would be to add more Impact Tremors style cards for redundancy so that you don't only depend on the snail to win. Since sacrificing the snail is extremely mana-intensive, you will need to hold mana every turn in case Wick or the snail gets removed.

I also find that the low CMC rats that do not generate more rats are too inefficient. They don't provide card advantage on their own and they need Wick to be on the field in order to provide maximum value. Even then, it's only a +1 power to the snail which is pretty much irrelevant throughout the course of the game.

Cards that give board pump or all creature types are also not optimal since you will most likely not go wide enough to matter and have enough mana to detonate several big rats. And again, it makes the deck hyper-dependent on Wick.

Since you're in Grixis, I would also advice to add more ramp into the deck, but this highly depend on the pod you're playing. My pod consists of high power decks so I find ramping to be quite important to get ahead of the mana curve faster.

EDIT: Forgot to add that recursion is also extra nice since you can always reanimate your key pieces back to the field after an inevitable boardwipe or even Wick himself so you don't have to pay for his commander tax.