The best alternatives to Duckey are SketchKeys, StiKey, and Emoji Keyboard by LINE. If these 3 options don't work for you, we've listed a few more alternatives below.
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EmojiFinder is the fastest way to type and find emoji meanings on your Mac! Start EmojiFinder from any app by pressing any shortcut you defined (the default one is ^⌘Space), type a word and check all the related emoji.