One of the first additions to the army was a unit of four Mournfang Cav, when these first came out I wasn't that impressed but the models grew on me and once I tried them out in a game I was hooked. They can be insane, especially when armed with an Iron Fist (for a 2+ save) and the DragonHide banner for breathe weapon goodness, it also allows you to re-roll 1's on your to-hit, to-wound and save rolls on the turn you charge, this doesn't sound too bad, but when you see it in the game it can add four or five extra wounds which really help and combined with the breathe weapon can turn a combat in the Mourfangs favour, even against a ranked up unit of infantry.
The next addition to the army will be a second unit, mainly because I have a bunch of the Forge World Rhinox riders and want to use them, and the only thing better than one unit of Mournfang is two units of Mournfang.
The first unit is nearly finished, just the banner bearer to go. After this I will probably try and get the Stonehorn painted up. I have a Thundertusk done but in the two games I have played it in it hasn't really performed, so am going to try the more simplified approach of Mournfang + Stonehorn, point them in the general direction of the opponent and charge. Either it will hit and destroy or they will get bogged down and die, but if that happens its fine as there will be a bunch of Ogres following up. The Stonehorn is also less likely to get taken out by Cannons before it reaches the opponent due to its rule of halving wounds taken from multiple hit attacks, it won't get taken down in one hit which means it will get into combat (assuming it doesn't get hit by two cannons of course).