In early 2010s, two gas and gas condensate fields were discovered in a South-East Asia Basin. The Field Development Plan (FDP) was approved to develop both. After drilling several wells, the operator encountered complex challenges: (1) lower permeability reservoirs (2) complex HPHT subsurface structures (3) fluid identification, (4) reservoir understanding and connectivity. Formation evaluation, especially formation testers were therefore crucial for better reservoir understanding, to de-risk the FDP and maximize future productivity of the field. This paper will discuss formation evaluation and formation testing in this campaign which consists of more than 10 jobs. Firstly, proper pre-job design and planning was done based on reservoir fluid information and reservoir properties from the previous exploration campaign. Analytical and numerical simulation models were conducted to properly design the Formation Tester (FT) tool string: probe/packer types, pump rate, and displacement unit types. Later, logging operation procedure, real time monitoring, and communication protocol will be also discussed with lessons learned and best practices. This workflow has set another milestone for fit-for-purpose solutions to tackle the reservoir and operational challenges. In this campaign, apart from a new discovery, based on Downhole Fluid Analyzer (DFA) technology, we surprisingly proved different fluids in the deeper reservoirs. In addition, we were able to address reservoir connectivity, the main uncertainty in their FDP. This paper also discusses several innovative methods associated with FT technology to reduce uncertainties in the FDP such as: The FT selection to help obtain best reservoir data, even in the most challenging environments such as low permeability, uncertain reservoir fluids, HPHT, and complex subsurface structure.As no well test was planned, Interval Pressure Transient Test (IPTT) data was used to obtain zone permeability which was later used to calibrate petrophysical data and the dynamic reservoir model.The use of pressure and DFA data to understand reservoir connectivity. The comparison between DFA data and PVT lab results will be also discussed.The use of advanced reservoir simulation software to understand reservoir contact uncertainty and improve reserve estimation. From this work, we have learnt that collaboration between different teams and disciplines is most important for this to be a smooth and seamless operation. Innovation and sustainability workflows are always possible to adapt in order to achieve good results even in the most challenging environments.