BioShock 2

To achieve an A rank in each trial you need to earn approximately 90 % or better of the available Adam in the original 18 Trials. The longer your little sister harvests without interference the higher her multiplier climbs, to a max of 4x. Ideally stay near her the entire time so if any splicer does get close you can attack them to stop them from attacking her. The first attack a splicer does gives you a warning that your Little Sister is under attack, every subsequent attack removes a multiplier bonus.

The tricky part is moving to and from the vending machines which leaves your little sister defenseless while you are away. Use any available traps to protect her and get back and forth quickly. Cyclone traps, mini turrets, trap rivets and proximity mines are all excellent examples. Remember your Little Sister is immune to all damage so don't be afraid to shoot a grenade right on her. The Decoy Plasmid is also reasonably good at distracting splicers.

Brute Splicers and other Big Daddies never attacked the little sister while I was playing the trials. They are solely there to try and kill you. Remember to keep your eyes open while dealing with them to ensure that a regular splicer doesn't weasel in and attack your Little Sister.

Always hack all vending machines before you start so you have cheaper prices on ammo and health kits and always hack health machines, many times a splicer would run off and never return just because I took the 2 minutes to check the level and hack the 1 or 2 health stations.

Overall this was not a hugely difficult achievement, primarily just remember to watch your health and above all keep your little sister untouched as much as possible. Each trial has a reasonable load-out so killing splicers shouldn't be overly difficult. Remember your plasmid abilities too, Electricity in water, Fire in oil. That always helps :) Once your Little Sister has finished harvesting any remaining splicers will continue to attack, however picking her up immediately ends the trial so as soon as she is finished make sure to pick her up especially if you are low on health. Additional kills net you no extra gain.

Lastly I wanted to mention one specific trial. In the 5th area the third trial gives you 4 Level 3 Plasmids, Electro Bolt, Incinerate, Cyclone Trap and Decoy and 4 Plasmid Boosting Tonics. You have no guns. Additionally you get no money from killing splicers, this means the 3 Health Kits you start with are all you get. I had a harder time staying alive than I did protecting the sister, primarily I used Cyclone traps and Decoys. This trial may take some practice. Don't forget you can charge up to 6 Cyclone traps with special abilities, ie Fire or Electricity, to use as traps.

Good luck everyone!

Edit: Clarified only the original 18 trials, the bonus trials have a seperate achievement that is not rank based. Thanks Drummin!

Collect most of the ADAM on all challenges to earn an A (90%). You can also earn an A+ (100%) if you do even better and if the little sister was untouched. Not too hard, only a few are challenging but most can be solved with common knowledge or thinking ahead of time and placing traps everywhere.

Note: If you are having trouble with the "No Guns" challenge, pay attention to your perks/tonics. If you sit in the water your health and plasmids will regenerate. Problem solved.

Good Luck!

Just a useful note, if like me while play the trails, for what ever reason your plasmids won't cycle through ( I got all the way till 5-3 which is impossible with just cylone)

what you want to do is go to your memory on the dashboard and delete just the protector trails DLC and re down load it, that should work. Work for me last night. You don't lose any progress either to your trails so all trys you have completed will not be all for not!

Hope this helps!