Out of everyone, I think Tenshi might be the scariest
Tenshi is basically second only to Yorihime in terms of power level. She's defeated Reimu, her skin is tougher than steel, and her sword can cut anything "no matter what."
She's normally got a very pleasant, if aggressive, personality, so when she gives you a death glare like this... it's scarier than Yuuka.
Tenshi is basically second only to Yorihime in terms of power level.
Except, she's not. Zun actually has engaged in power level discussions with Touhou fans during his infrequent visits to Japanese image boards. When asked about how strong Tenshi was, due to her quotes, his response was something like:
She is about equal with Yukari, in terms of strength and power.
Ironically, this means she is (possibly) a lot weaker than Yuuka. Why? Someone asked Zun once about a potential match up between Yukari and Yuuka, Zun's response was simply:
Gap <<<<<<<<<<< Youkai Moe
Of course, there is the notable chance that he was joking around, but it could underlie something else about the characters.
Honestly, I would still be more intimidated by Yuuka. At least Tenshi understands and respects the Spellcard rules, more or less. Yuuka? When asked why Yuuka did not have an entry in The Grimoire of Marisa, Zun's response was basically:
There are some people that just absolutely refuse to abide by the Spellcard Rules. Usually these are convinced to agree, but there are a few that nobody can force. Yuuka is one of these, so it is natural that she doesn't actually have any (spellcards) for Marisa to write about.
So, if Tenshi is giving me a death glare, she may leave me alive. If Yuuka is, however, I am fertilizer.
translation fix: While トスン expresses a rather light impact while ドスン expresses a heavier sfx. This is probably because of Tenko's chest being rather solid than soft and her iconic attack aside from her blade consists of stone tossing/dropping.