Deck is great. Very explosive and has great flexibility with enough removal for most decks. The general idea is to buff Cohen with an offering and then hit him and witcher trio with Allgod. The fifth buff can go anywhere, but I like to hit Mad Kiyan, Geralt Quen, or Berengar if a big body is useful in the matchup. Then you play trio into Cohen and leader in the same turn. There are exceptions, but stick to the plan for the most part.
Running through the list.
Some people use Amphibious Assault over Oneiro. That's fine, but it only really grabs Cohen and your bronze dudes. This deck is considerably worse if you don't have access to Allgod on time. I also like being able to offering and grab tall punishes and trio when necessary.
Geralt Professional I've found to be better than the other choices, but I won't die on this hill.
Eskel is mandatory. Being able to snipe awkward units (not relicts or witchers) and getting ahead on board is a huge deal. Worst card in the mirror and against relicts.
Vesemir and Quen don't need much of an explanation, don't forget to have Adrenaline though.
Mad Kiyan I just like this card. You could play Keldar over this and sub Professional for Geralt of Rivia. This package has served me well though. Kiyan ideally doubles your extra pump spells if they've got a unit to hit. Don't kill their guy unless it's an emergency.
Trial gives you some flexible removal, but also just plays for 11-12pts on small witchers.
Berengar you need to be careful with because it sacrifices the beginning of your turn. If they have movement you can be put in an awkward spot. It is useful to just have a big body sometimes.
Selective Mutation is awesome, just a tutor that leaves a couple bodies.
Griffin Witcher is kind of messed up. This is generally your stratagem target, If played on turn 1 he deals up to 18pts for 5 provision plus his own power. The veil prevents him from locking himself when he gets adrenaline making him a 3-4pt engine depending on if you pass. Sets up offerings as well. If against monsters play around Pred Dive with Mutation, All G, Quen, etc. Most of the other things that can kill it don't trade well with a 5p card. Heatwave and Vilgefortz come to mind. Do note that his order doesn't work when moved, but his passive still triggers at the end of the turn.
GW Adept is also pretty gross. This guy is very difficult for decks like Frost or Bleeding. Invalidating their damage while building your board is a good thing to be doing. I will just lean on 1 of these per round in those matchups. If on the Keldar build and he isn't immediately answered, these guys get especially nutty.
GW Mentor has consistently overperformed for me. Hand-fixing is so powerful in this deck because if you miss on trio or Cohen you lose....probably. The boost does change how you leader sometimes, but a very worthy inclusion.
Target practice is just what we have access to. Usually the worst card in the deck, but makes Kiyan bigger and gives us Adept fodder.
You also have a Thaw for the second GW. Some lists run Mahakam Ale, but I find both to be pretty mid.
Playing the deck.
This deck actually likes to go first. The extra mulligan is a big deal because it is illegal to All G without full trio and Cohen in deck. The mentors also help ensure these guys are where they need to be at any given time. Also Crystal Skull is busted and developing a GW early helps control the board.
During mulligans don't be greedy. If you have access to All G and all 4 of the boys are in deck don't risk the last mull. The bronzes are quite good and can easily carry you through most round 1's.
This deck can 2-0 a lot of decks a couple cards down, but also can play all 3. There are decks you don't want to see in a long round 3 so use discernment on when to push. Often, You want to hold trio and Cohen for the last two plays, but there are exceptions. For example, Handbuff can't easily mess with trio's power so you can run out trio and Cohen and save your tall punishes for a big Torque and Aglais.
Be careful how you stack rows on the big round. With All G, 1 offering, and Vesemir: Mentor played the boys are coming out at 7. I would take some time thinking about how to maximize leader here. You want as many units to have the same power as Cohen. Never float Cohen, he will get answered and you should lose the game. Also you lose to Igni and Scorch. It happens sometimes. Villentretenmerth can get you if you spend your Eskel so be aware of that.
Only had time for one game this morning, and it was the mirror. Awkward set, but hope you enjoy.