And a warning (this is mentioned on the reference cards, but I thought it was worth mentioning).
On the Teensy 3.5 the inputs are 5V tolerant.
On the Teensy 3.6 the inputs are NOT 5V tolerant. Max voltage is 3.3V.
It turns out that on the Teensy 3.5, only pins with digital I/O are 5v tolerant. A10, A11, A21, A22, A25, A26, AREF, Program and Reset are NOT 5V tolerant.
All of the pins listed above and any pin in analog mode should only get 3.3v max.