I've seen the disparaging sense of sucks as a verb ("sucks to be you", "that sucks!"), but this particular usage from Price Caspian seems a little odd:
Lucy heard Edmund say, "No, let me do it. It will be more of a sucks for him if I win, and less of a let-down for us all if I fail."
My interpretation was that It'll be a sucks for him is intended to convey "It will be a victory for us", with strong implications of humiliation and embarrassment for Trumpkin.
However, I can't find a dictionary definition which quite matches this use of the word.
eat crow, Informal. to be forced to admit to having made a mistake, as by retracting an emphatic statement; suffer humiliation: His prediction was completely wrong, and he had to eat crow.