Like in the screenshot, Horse spawn eggs can spawn donkeys and mules. This should not be intended because donkey and mule spawn eggs were added into the game in 16w20a.
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Relates to MC-102059 (they probably should be merged and info about zombies should be added, or they stay separately and ticket about zombies should be added)
Updated MC-102059
Also zombie and skelly spawn eggs can produce husks or strays