https://pobb.in/KIqJ81czes8l

This build capitalizes on Ngamahu, Flame's Advance burst window with Frozen Legion and Tawhoa's Chosen. Both attacks benefit massively from slow attacks and have great synergy overall.

My assumption is that Frozen Legion alone isn't enough and requires an additional skill to fill the gaps. Ice Crash is the obvious choice because it' scales damage the same way Frozen Legion does and a slam is required to trigger Tawoha.

100% of cold damage is converted to fire via Cold to Fire support and Avatar of Fire. This allows the use of Hatred. Alternatively Cold to Fire could be replaced with Trinity (probably with Staff/Axe and alternate ailments) but I didn't investigate further.

Despite potentially having access to 2 x 6L, the build is very starved for gem sockets. To combat this a Hypothermia (shaper mod)/Essence of Horror (30% ele dmg) helmet can be used for Frozen Legion. Mace mastery "all damage inflicts chill" enables Hypothermia. Leap Slam cannot be use as movement skill because it triggers Tawhoa.

Tasalio could be replaced with Arohongui for generic defence and offence, and it might allow for more overlap of Frozen Legion. Valako could provide more damage but requires Molten Shell to be replaced with Immortal Call. I doubt inconsistent access to Endurance charges beats Molten Shell.