Accurate measurements and identification of jets, missing energy and boosted hadronic resonances are crucial to most of the ATLAS physics programme both in domain of Standard Model precision measurements and search for beyond the SM physics. The ever increasing LHC luminosity while providing higher statistical sensitivity to rare processes, also leads to more challenging experimental conditions due to multiple simultaneous collisions (pile-up). Additional energy falling inside a jet cone can affect both the jet energy scale and resolution leading to performance which depends on the amount of pile-up. Missing Transverse Momentum, formed from all reconstructed objects, is particularly affected by high pile-up. New techniques are developed and presented to improve immunity to the effects of pile-up and maintain or improve resolution and identification capabilities despite more challenging conditions.