I'm not grinding LoR much till the patch but I have managed to get back to the top 200 (@150 right now) using this MF/Sej deck playing very casually the past couple days. IMO this version is the best MF/Sej deck. I love it. It can win against everything. Burn is probably the toughest match. My biggest win was CRUSHING a rank 17 Master player.
I think after the update you'll see this type of deck even more rampant. It's practically an aggro deck with a massive late game. And it's annoying as fuck due to Pilfering.
Some of my annoying losses are due to getting pilfered and they take all my good shit from me.
CEBACAQBAIFQEBQFBMIRIFQ4EETC2MJ2AIAQCAIWAEBAMHIA
https://lor.mobalytics.gg/decks/br6a4ctbunq8v05pena0
Building the deck:
I basically threw in every OP bilgewater card and only 5 Freljord cards.
I've been testing Sej everywhere and this is where she really shines. You can VERY OFTEN have her leveled by the time you can play her. I wouldn't say it's a goal, but it just happens naturally so often. And when she's leveled, it's almost game over. Because with Warning shot you can trigger her effect and prevent the opponent from ever killing you. If they Will of Ionia, you Warning shot during the response, it spoils their attack phase, then on your turn you can just replay her. It's the most annoying toxic shit ever. And if you can have an MF on the board as well, oh boy.
Originally I didn't have the 2x Salvage but adding them has sealed up a huge weak spot. Without them, you run out of gas... which sounds weird due to all the pilfering, but you actually really need to cycle YOUR deck.
You'll see other versions including Fury of the North, which is a good addition, but I've intentionally kept it out to have a higher change of hitting with Yordle Grifter. I just love having the high consistency of 3x on almost all the cards.
Mulligan for 1s and 2s usually. If you go first, getting the attack on the first round really helps speed up leveling Sej. If you go 2nd, you pray your opponent misses their 1drop so you can open attack next round and get a nice Plunder in, or force them to use a Mystic Shot or something on your Hawk/Butcher. Playing Butcher as a 2/2 on turn 1 is definitely correct.
Hoard Warning Shots for Sej / Citrus / Rex turns and try to get plunder activations with Make it Rain / MF / Zap beforehand. If you have a load of Pilfereds/Black Market Merchants, then obviously use a Warning shot to trigger a big Pilfering turn.
Let me know how it works for you, I've been having a blast with it.