This solution of mine that I will give you must play with a friend of yours, in case you do not have a friend who owns this game I recommend that you see the solution of tornprince2012. If you have any friends that have this game and can help you recommend you to read and use my tips. Let's go to the solution.
. I recommend SERIS character for this achievement. And I'm warning you that it's not very cheap to unlock her.
. You should do the following, look for an unbound siege match, because this and the match that takes longer to finish, for this achievement you need a lot of time.
. You must select the character SERIS, and your friend the character FERNANDO, because he has enough life.
When you start the game, your friend should stay close to the goal (not inside it, so you capture the goal and lose time), and you stay behind him in a place protected from enemies healing him (healing others of the match as well, but your main focus is your friend). Then when your friend is low on life, ask him to take the shield and hide, so you can heal him very easily.
. On the selection of cards for Seris, I recommend seeing the guide from tornprince2012.
. Remembering that FERNANDO has 5000 lives if I'm not mistaken, then you healing the ja gain a lot of advantage to reach 100,000 and unlock the achievement.
. In the parts that I told your friend in this guide, I am referring in the character that he is playing, the FERNANDO in the case.
. Let your team take care of the goal, you just concentrate on the achievement, if the enemy team captures the goal, then FERNANDO goes to defend and prevent the enemy team from winning, and SERIS only focuses on healing.
. Probably if a team can do 2x0, in case you capture the target and manage to push the wagon to the enemy base, you probably will not be able to unlock the achievement. Then you will need a few tries for that achievement.
. With my friend, I was lucky to unlock her on the first try using these tips, in regards to luck, I was lucky because when my team captured the goal, they failed in the attack, and so went 1x1, 2x2, 3x3 and etc. . I was able to unlock the achievement when I was 3x3 for each team. And in the end I healed 108,000 of healing.
Sorry for the long solution, I tried to do my best to explain it right, any questions ask in the comments, and in case you have a negative vote, explain why in the comments.
Just remembering that you will need some attempts at this achievement.