Titan Killer (Plasma Railgun)
using this is a pain in the butt, but having a friend will make this less of a challenge. Make your friend damage the enemy titan (make sure it's a 2v1) and when it's near death make your friend back off and let you go in for the finishing blow. Another scenario is you not having a friend will not making this easy, but stick to a friendly titan and charge your plasma rifle then wait until your friendly weakness the enemy titan at the right time and then you steal his kill (you have to be accurate or everything can go wrong) after defeating 10 titans with the plasma rifle you are able to unlock the instant-shot which shoots like the 40mm rifle just with very low damage but can be still work very easily rather than charging it for full damage. The rest is up to you to get the 50 kills.