A little hint on how to get really high numbers. One of my creatures, however, died after a while. May they die after exceeding a specific number. Or it has to do with subtraction/addition.
Spoiler:
Use the ability to get double attribute on the follower which changes life with attack. In case you'd like to optimize it.
Place the ability: "Take the ability of the next follower recruited" and use it on the follower which changes the attack with the life every time he is attacking.
Then recruit the knight which can get 4 abilities. After that, you can place the double attributes ability, attacks two times and either add one life this follower each round or get the attack damage of the follower with the highest attack damage. Don't use both, since the gap is important!