If Day 2 was a technically tiring day, Day 3 was a mentally tiring day then Day 4 is the physically tiring day.
For this day it's you, a fellow candidate and 1 assessor. From people I've spoken to you do tend to be in Ogwen. We were on Tryfan, but you could easily be on Glyder Fach or Idwal.
You get told in the car park which route they want you to get them to and then the assessor will expect you to lead them to the base. On the walk in is where you get to express your knowledge of Geology and fauna. My recommendation is not to wait to be asked but just butt straight in there with your spiel. They don't expect you to be an expert but you need to have some idea of how the mountains were formed, when the last ice age was etc. Similar to ML but just a bit better. On the Fauna front, I didn't (and still don't know) the names of all the flowers in Latin. Some people do and some don't. That's really not important. Was is important is being able to know your Harebell from your Butterwort and know a little bit about the plants and flowers. For example, Butterworts are carnivorous flowers as is the Sundew; Club-moss is where coal comes from. You just need to know the basics.
Get to the base of the route. Rope up (the assessor will be second on the rope) and set off. THE MOST IMPORTANT ASPECT OF TODAY IS ANCHOR SELECTION. A single sling over a block is allowed as long as the block is solid and the sling won't walk off the top. CHECK EVERY TIME. If you are going to use trad gear as anchors then a minimum of two is a must. Even if you have a solid size 10 hex perfectly cammed in a crack, direct belaying off that will get you a shoeing. Two pieces in the same crack however is fine!
If you are slightly dubious about the anchors then DON'T DIRECT BELAY off them. This is all common sense stuff, but in the heat off battle it's surprising what silly errors you make. On my assessment I did half the scramble and then the fellow candidate did the other half. You are not given any guidance as to where to go, you are expected to follow the guidebook route description. When you get to the top then the assessor tends to direct you where to go down. This is probably because they are heading towards a specific lower. You will need to get your clients down technical terrain. As an example I got to go up Wrinkle Tower and then down Bastow Buttress. You have a lot of ground to cover in a relatively short period of time and you'll need a good level of fitness for this day.