ER229 MEXICO. Mint Error -- Struck with two tailed reverse dies -- 5 Pesos, 2018-Mo. Mexico City Mint. PCGS MS66. KM-605. Many collectors consider mules -- coins struck with mismatched dies -- to be the proverbial Holy Grails of mint errors. Two heads or two Reverse error coins are always sought after by error collectors. An undated 25C Washington Quarter Mule -- Struck with Two Reverse Dies -- NGC MS64 recently sold for $84,000 USD on Nov 13, 2025.