It's not sudden for me, it's just that I have hundreds of half-done plans floating around all the time (I really need to get better at making progress!).
Yes, I mean horns to the elves riding them. Those stags themselves are quite good- though mould lines can be a problem. You'll also find you really need to bend the stag antlers if you want to get them to rank up, and it can be hard to do that neatly without leaving marks. My suggestion is to go over the main body of the antler with some liquid greenstuff- focussing on weak bits or mould lines you just can't get to.
These are my riders so far, shown as a step-by-step. I don't like most of those rider models, so with few exceptions I only use this one sculpt.
I cut the spear from the leg, and file away the shield (which is a weird two-layer thing). Then I drill through the head, and insert two strips of thin fuse wire (going more complex than this was just too tricky). I bend them into shape, then cut them, then coat them in liquid greenstuff (also sealing them in the head). Then I sharpen the spear (the sculpt is very thick and blunt) and bend it how I want. This usually breaks the shoulder or elbow joint, so I glue and re-sculpt that (again with liquid greenstuff- it's too small and weak for much else).
Still to come is sculpting the helmet and building up the shield detail, plus whatever accessories I can think up/manage to sculpt.