A recent change to the iOS version of MAA has greatly reduced the chance that attacking an enemy will cause the enemy to drop anything whatsoever. While this may seem like a welcome change over collecting an Antitoxin from every other enemy you attack, in fact this change has become quite problematic for players (particularly higher level ones) when a new Chapter is released, because it has now become near impossible to complete the required task to obtain a certain number of "key items" to unlock a particular mission within the chapter. In the past, one key item was guaranteed to drop from every battle, but now the key items have a low and variable drop rate like all other items.
Traditionally, it has been suggested that the player should use heroes with attacks that hit multiple times and have a high chance to crit to increase the chance at getting items to drop. Multi-hit attacks on enemies is not a good enough solution for high-level players who get a new story chapter because, because while multi-hits increases your chance-per-turn at getting an enemy to drop an item, the problem remains that you basically only get one chance per enemy to get a drop because you've killed that enemy after one attack.
As such, I'm going to give the following advice to players, such as myself, who are trying to play through the story missions:
- Needle Gun
- Emma Frost
- Healer (eg. Iron Fist or Dr. Strange)
The tactic is as follows:
Attack only with your Agent's Needle Gun, which will let you take a vast number of pot shots at each enemy. Preferably equip tactican armor on your agent to get extra turns against blaster enemies.
Use Emma Frost's Unlock Potential whenever it is available to restore everyone's Stamina and remove any debuffs you may have acquired, otherwise just skip the hero's turn with Recharge.
Use your other hero's healing ability whenever you've been injured to keep everyone alive to stretch out each battle as long as possible.
Eventually, one of the enemies will drop the item that you need. Then you can keep poking at enemies for other drops, or just one-shot all the enemies and move on to the next battle, because I've never observed a battle where the special items drop more than once.
The net result is that, first, you will have a lot of chances per enemy to try to get the needed item to drop, and second, your mission score will be extremely low to prevent five-starring a mission the first time you run through the mission.
The down side is that missions take a heck of a long time to finish this way. However, since I've adopted this method, I've managed to acquire all the necessary key items in a single run through a given mission (at the cost of a small portion of my sanity).