If you do, put that many +1/+1 counters on it
And don't worry: MTG Arena is aware of how many copies of a card are useful to you and will prevent you from crafting more than you need
Life is good! And if youve got a well refined deck, that number can be 2242, meaning you will have completely defeated Arzakon and his 100 life
If Faunsbane Troll is no longer on the battlefield or no longer a creature when its activated ability resolves, it doesn't fight the target creature, but the effect that causes the target creature to be exiled any time it would die that turn still applies
If you can make a lot of tokens (say, Mites), Flesh-Eater Imp can become as big as an Eldrazi- an Eldrazi that can instantly end the game for someone
Of course, this doesnt mean that these cards will all be powerful