Two-handing weapons in Elden Ring Nightreign is an effective technique to deal more damage and defeat bosses.
To two-hand in Elden Ring Nightreign, hold the Triangle or Y button and press L1/LB or R1/RB to set the weapon in the left or right slot as your main weapon.
Two-handing a weapon increases your damage output and chance of critical hits, but requires more stamina for attacks.
When using a bow with both hands, it allows for Precision Aiming mode, but it's best to avoid during important fights due to reduced movement speed.