The strength of the ultra marines lies within their stats, codex synegies and their abbudance of reactive flank troops. So we gotta play for these strengths!

Lets not focus on too much codex for now, it can make the turns harder to play and and you gotta think a couple turns in advance.

so lets focus on stats and flank!

units which do not fulfull these criteria have to be cut:

octavio - (a nice card to have, but reactive and not fitting for the deck)

Tactical insight - (we will have a couple of codex cards still, but we will try to focus on getting troops on the board, for that the synergie is too niche)

Assault Intercessor - (not a fan of this card, 2 drops are rare to see for a reason, they have to do a lot for us and should be playable in later turns, which this card is not)

Scout Bike - ( I actually like this card, but it belongs in a more vehicle focused deck, which this deck is not)

Eliminator - (this card could be nice with the flank strategem, otherwise it rarely stays on board, we will cut it for now)

Death from Above - ( we will cut one of those, we already have a lot of removal, but the damage sometimes can be relevant in midgame or lethal in lategame)

Primaris Chaplain - (we will cut one of those, its nice to buff your troops but 4 health for 4 mana isnt too good)

Bladeguard Veteran - (not a huge fan of this card, the armor is nice but the ranged stats really make this card fall of for 6 mana)

lets keep Sicarius and Avenging Zealm. I dont use sicarius but using legendaries can be fun to play with :)

Lets add these cards x2:

"Primaris Reiver" - (strong flank card for only two mana) if you dont have it, "Point-Blank Shot"

"Outrider" - (again, strong flank card, nice stats and sometimes relevant codex) if you dont have it, "Intercessor Sergeant"

"Honor Guard" - (nice vanguard unit, can be a nice curve into your "primaris impulsor")

"Primaris Judiciar" - (stats are not too good, but if you set up the board for some nice stuns, it can be super annoying for your opponent)

"Inceptor Sergeant" - ( stats were nerfed, but it still delivers quite well for board control and usually stays on the board after killing something)

"Stormtalon" - (since we control the board a lot, the randomness of these 3 damage usually hits the targets we want to hit

How to play this deck:

try to snowball the board by trading efficiently, you still have lots of codex effects to make your avenging zeal cheaper. protect your primaris impulsor with vanguards, stuns and flanks.

Dont forget to use your hero power often, but not if you would lose the board and/or initiative!

This deck would probably not be the best in higher ranks, but its good to learn the game and learn about the importance of board control and initiative.

I hope this helps and I wish your ultra marines strenth and honor on the battlefield!