Final Answer:
Wilbur Soot built a new flag out of obsidian and magma blocks for Manburg.
Step-by-step explanation:
Wilbur Soot: The individual responsible for creating the new flag for Manburg is Wilbur Soot. This aligns with the direct mention in the question.
Built a new flag: The action performed by Wilbur Soot was the construction of a new flag. This indicates a creative endeavor related to the symbolic representation of Manburg.
Out of obsidian and magma blocks: The materials used for the flag's construction were obsidian and magma blocks. These details highlight the specific components chosen by Wilbur Soot for the flag, showcasing his creative decisions in the process.