In a manner that causes addiction or in a way that is compulsively engaging; with quality of being addictive.
From 'addictive' (adjective) plus adverbial suffix '-ly,' which turns adjectives into adverbs describing how something happens or behaves.
The adverb 'addictively' lets you describe behavior itself as addicting—'the game is addictively designed'—making addiction about structure, not just personal weakness.
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