You must use all 25 in one match. There is a lot of speculation on what is the best method. Some people like to go from area to area only focusing on collecting the power-ups. Other people like to capture flags which earn you mutators as well as pick them up. The problem with these is not only your enemy, but your team. They will also be going for the power-ups and collecting the flags making it very difficult for you. Luckily, there is one Tier 2 mutator that can help you with this achievement. It is called "Wild Card". When you use it, it will give you more mutator options. So if you end up getting this mutator, it will actually count as 2 since you will have used both. This is the sure fire way to get the achievement, but it will take some extra playing because they cost points and you're already wasting the majority of your points on a Tier 3 mutator. This will hopefully be fixed soon with a patch (the glitchy cost/spent point system).