Generally, I'd spend my charms like this: gold, green, crimson and then, finally, blue. For gold, spend them on barker toads. For green, ibis are pretty good (or at least used to be), but I spent mine on unicorn stallions when I trained it. For crimson, I'd change it whenever possible unless it's a scarce secondary ingredient or too expensive. For blue, I'd wait until I could make geyser titans. Hoped you find this useful! Best levels in summoning, in my opinion: 52, 67-69, 88, 96, 99