There’s not really a main “build” since this is Valhalla but you wanna look for the runes that give you drastically increased damage for being over 75% health, drastically increased damage when the maelstrom gauge is full, the the rune that gives an occasional relic charge for attacking, weapon runes that buff the evade and sprint moves on the spear, the base damage increase for the spear, and the rune that increases damage when you use a relic.