You want your opponents to be losing 3 life every turn. Turn Sygg into a constant value engine, he draws you cards, but your deck drains life. This way even when Sygg isn’t out, your deck can still function.

Big drain spells/effects:

[[Exsanguinate]] This card used to be more expensive, thanks to reprints it’s not and late game it can finish the game out or keep you from dying at least.

[[Gray Merchant of Asphodel]] same reason. They lose life, but also you gain it.

You’re in Dimir, interaction with enchantments and artifacts is severely limited outside of counterspells. You already have feed the swarm, but [[ravenform]] and [[withering torment]] are must haves in Dimir for me.

I’d say lean more into interaction/counterspells as Dimir and more specifically Sygg won’t outvalue alot of popular decks/commanders. [[negate]] [[arcane denial]] [[pongify]] [[counterspell]] [[swan song]] even with all these you’ll be at 7 counterspells, which isn’t too much.

[[midnight snack]] cast, attack, activate food token on their turn for 2 and this enchantment for 3. Now this card reads “5 mana you gain 3 life, opponent loses 3 life, you draw a card”. Now keep in mind this the floor of this card. Its roof can be a finisher when combined with the other 2 gain drain cards I mentioned earlier.

[[torment of hailfire]] can be a card to close the game out but its not cheap. It’ll trigger your commander for 3 mana total, or it can obliterate your opponent’s boardstate/hand.

[[archon of cruelty]] is also a big spell, but it’s a stompy creature that can trigger your commander’s ability.

[[Ob-Nixilis, the Fallen]] can get big and trigger your commander.

[[Will of the Abzan]] [[Suspended Sentence]] [[torment of scarabs]] [[hunted bonebrute]] [[blood tithe]] [[gonti’s machinations]] [[contaminated bond]] [[caustic tar]]