As long as any creature is unblocked during combat, you can ninjutsu in a ninja with said ability
Next you can go either two ways, If you have any of the most expensive MTG cards, you can get in contact with us and we can make you an offer for your cards based on condition, or you can send your card to be professionally evaluated
The earlier the better, even if negotiations are in progress
They're used to create different effects and interactions between the cards
20 damage isn't a lot, obviously, but how often have you faced someone who sends seriously weakened powerhouses to the bench for a well-deserved rest
As this is Part 2, I'm assuming you read Part 1