Braxis Holdout is not a good murky map. Murky is a late game hero and Braxis Holdout gives a huge advantage to the team that wins the first objective. I would recommend the standard slime build with the octo-grab ult.
A strategy for soloing against one other when the shrine is up is to bounce between killing mobs and capping the shrine. This way the enemy has to decide on whether to kill your puffer fish or to let you cap the shrine. Either way mruky wins!