The two promo cards are a must if you aim for high end of the leagues. I play (modern) diamond 1 and I regularly run into both, Mantaroth a bit more than Grimbardun. Mantaroth is a heavy hitter and hard to beat. I found Jacek works best against both, since the scattershot can kill the backlines first and then it is quite easy to finish the work. Even then my win rate against them is less than 50%. I only bought 30 packs in the presale myself and got 3bcx Grim, sold one to stake more DEC on land and sent the other to my bronze alt account.

Your plans on RB look good. I will have to get to mine as well, but currently I am still ~15 plots worth of DEC short for land which is priority over RB.

Great post, have some !PIZZA