Here are a few options depending on the context and nuance you want to convey:
For a charming, potentially harmful person:
* Alluringly perilous
* Enticingly risky
* Captivatingly treacherous
For a situation that's both pleasant and risky:
* Deceptively safe
* Temptingly dangerous
For something that's beautiful but potentially harmful:
* Stunningly toxic
* Enchantingly deadly
Ultimately, the best two words will depend on the specific situation you're describing.