Where the Letter B Breaks the Pattern
Most mathematical styles run A to Z in one unbroken block, but not all of them for this letter. Script capital B is โฌ (U+212C, Script Capital B). It was added to Unicode in the Letterlike Symbols block years before the mathematical alphabets, and the later block left a gap there instead of duplicating it. On some devices a different font draws this character, so a word set in that style can show one letter that looks slightly unlike its neighbours.
Small Capital, Turned and Other One-Off Forms
Small capital B is ส (U+0299). Like most small capitals in Unicode it was encoded for phonetic notation, not as a font feature, which is why small caps text pastes as ordinary characters. Unicode has no dedicated turned b, so upside-down text substitutes a character that already has the right shape when flipped. Superscript b is แต (U+1D47). There is no subscript b, so subscript text leaves that letter at normal size. The regional indicator ๐ง is half of a flag: two of them in a row turn into a flag emoji when they spell a country code.
Which B Is Safe to Paste
Bold ๐, italic, sans-serif and monospace forms display on nearly every phone and computer. Circled โท and fullwidth ๏ผข are also widely covered. Dark squared ๐ ฑ doubles as an emoji (the blood type B button), so many apps draw it in colour instead of black and white. Screen readers may announce a styled B by its full Unicode name or skip it, so keep anything important in plain letters as well.