If someone negated Otho's ability after he discarded an enhancement, does he get the enhancement back or not?
Yes.
If you negate an ability, you negate the whole thing including costs.
This is (almost) always true. But, for example, if you played a card that said: "Do X to do Y", and I played a card that said "Negate abilities that do Y" then you would negate Y without negating X. However, I'm not sure if there is a real scenario in the game that would cause that, but if there was, then that's how it should be ruled.
