A legendary item has this feature . . .
Legendary Surge: All legendary items have a legendary surge ability, similar to a mythic character’s surge ability. It can be used only on specific rolls or checks based on the nature or purpose of the legendary item.
The legendary surge ability allows the bearer to add the result of a d6 to the appropriate type of roll or check. A mythic bearer can use her surge die type in place of the d6. If she’s bonded to the item, she can increase that die type by one step.
Simple enough the legendary item has a D6 surge, if the weaerer/bearer is mythic they can substitute their mythic surge for the legendary surge and if they're bonded to the item they can increase the die tyep by one step. Mythic surge is . . .
The monster can call upon its mythic power to overcome difficult challenges. It can expend one use of mythic power to increase any d20 roll it just made by rolling 1d6 and adding the result to the d20 roll. Using this ability is an immediate action taken after the original roll is made and the results are revealed. The bonus die gained by using this ability increases to 1d8 at 4th rank, 1d10 at 7th rank, and 1d12 at 10th rank.
Most of this is again clear if your rank 1-3 you use a d6, 4-6 a d8, 7-9 a d10 and 10th a d12. If your using an item your bonded too that increases by 1 step e.g. a rank 4 could use a bonded items legendary surge ability to add d10's result to their role (rank 4 = d8, bonded item increase by 1 step to d10). What I'm not sure of is what happens to a rank 10 using a bonded item. Do they not increase their d12 as there's no next step, increase it to 2d6, 1d20?
Anyone know an answer to this?
I assume you're supposed to use the dice size FAQ for this:
Size Changes, Effective Size Changes, and Damage Dice Progression: I'm confused by how to increase and decrease manufactured and natural weapon damage dice when the weapon's size or effective size changes. There's a bunch of different charts, and I'm not sure which to use.When the damage dealt by a creature’s weapons or natural attacks changes due to a change in its size (or the size of its weapon), use the following rules to determine the new damage.
• If the size increases by one step, look up the original damage on the chart and increase the damage by two steps. If the initial size is Small or lower (or is treated as Small or lower) or the initial damage is 1d6 or less, instead increase the damage by one step.
• If the size decreases by one step, look up the original damage on the chart and decrease the damage by two steps. If the initial size is Medium or lower (or is treated as Medium or lower) or the initial damage is 1d8 or less, instead decrease the damage by one step.
• If the exact number of original dice is not found on this chart, apply the following before adjusting the damage dice. If the damage is a number of d6, find the next lowest number of d6 on the chart and use that number of d8 as the original damage value (for example, 10d6 would instead be treated as 8d8). If the damage is a number of d8, find the next highest number of d8 on the chart and use that number of d6 as the original damage value (for example, 5d8 would instead be treated as 6d6). Once you have the new damage value, adjust by the number of steps noted above.
• If the die type is not referenced on this chart, apply the following rules before adjusting the damage dice. 2d4 counts as 1d8 on the chart, 3d4 counts as 2d6 on the chart, and so on for higher numbers of d4. 1d12 counts as 2d6 on the chart, and so on for higher numbers of d12.
• Finally, 2d10 increases to 4d8 and decreases to 2d8, regardless of the initial size, and so on for higher numbers of d10.
Damage Dice Progression Chart