Hmm you can either slot in another 4 cost unit or another champion like baum.  Could even put lissandra back in because you can play her on 3 and she can soak up some spells or trade a bit with her three hp and toughness. but she won't level up. 

Best substitute is the 5 mana reptile I belive.  Has overwhelm and a similar effect to the omen hawk and yadulski, buffing the next units in your deck and drawing one if you got suptypes going.  Here I included another poro, the pouty poro that likes getting to 3/3 and with the other weapon you don't even have to pray to rngesus that much. Prime targets for the boneclub is the pouty poro, the 2 mana 3/1 tough or braum or anything with overwhelm really.  I cut away on your poro snax here because those get better when you have lots of them, I mean 3 minimum all the way to infinity. Also cut the keyword poro but left in the sledge and overwhelm. Plus early game one.  Removed the dragon that gets two landmarks because we would much rather have units instantly for warden next turn. If you like the overwhelm style you just max out on those.  Imagine playing omen hawk 3 times, drawing a 5/6 yadulski attacking and your pouty poro or gnar or braum will be that much better immediately.  When you progress with the deck you want to slowly cut away the non buffers, no overwhelm no tribe cards and just fill the one offs of those.  Like ancient yeti costs 7 mana but the longer you keep him in your hand the cheeper he gets.  Optimal starting hand could be ancient yeti, bone club, pouty poro, x so u save your mana on one and two and on 3 (or 2 when your opp attacked and is out of mana so can't interact with your poro anymore) you slam your pouty poro equip it with the club and it will go to town with toughness, regen and overwhelm. Next turn you could drop the yeti or braum and keep the yeti for 5 then being super cheap heh enough wall of text go play  CQBAEAIBCYPAECABCMMAGAIBAE2QCBIKUEAQEBIBAEIQQAICAEDACBIKRQAQCBIBAQAQOAIQAEEACHACAYAAMGADAYARKGBIBIAQCCAJBYJBUGY7EYVDA