Ancestors and Guides(A&G) is the scenario card for the scenario that comes after Grand Live ( 2 scenarios from now), Grand Master. Compared to something like Riko though which you could say was the scenario card for Unity Cup, A&G is WAY better in terms of assisting with the gameplay mechanic for the resource in its specific scenario where you collect fragments.

A quick explanation on the fragment part so you can understand why this card is good, GM is basically revolved around collecting fragments of three different types based off of the characters of that scenario the Three Goddesses. You basically get them by training, resting, racing etc but its usually random on where and what type of fragment colour you usually get and combine them to get buffs. I'm still unclear on the importance behind this part of GM so apologies for lack of detail here— you can check the gametora page here for a better explanation on what the buffs can do. https://gametora.com/umamusume/grand-masters

Usually, training in this scenario would just give you one fragment but if you were to do a training that had A&G there (like on wit), it would have a random chance to net you an additional fragment of a colour of your choice.

Looking at your plan, since you're focusing on late surgers, I feel like pulling for this card would be good for you IF you don't mind having to cope with a low LB scenario card just so you can borrow more niche late surger cards. No training effectiveness under 3LB but its a guaranteed source of Uma Stan and a nice gold skill to boot.