Please include the following information:

Which boss? (ex. Seraph)
What is the battle effect? (ex. Seraph that applies Frostbite to friendly units)
Which boss variant battle setup to use for the waves of enemies? (ex. Seraph the Chaste). Alternatively if you want a fully custom battle you can list the enemies per wave.
Stats? (Give him Sweep, but a much lower attack like 6)
Pact Shard Upgrades?

etc.

Use the information provided in the github repo and the Monster Train wiki for helpful pieces of information that would be useful for me.