|This build is meant to capitalize on Niles's decent speed and excellent resistance. The highlight of the build is his A skill, Flashing Blade, allowing Niles to charge his special more quickly in order to do massive amounts of damage.
+Spd is optimal for Flashing Blade. -HP is recommended over -def as Niles has a superbane on Defense and -res means less damage output and less targets he can Ploy. +Res can work if Niles takes full advantage of speed support, runs Spd Ploy, and/or Phantom Spd as his seal. His attack is already rather low and he does most of his damage is done via his special, so -atk is a fairly "safe" bane, though he may not be able to kill as many of the low def ranged units he could otherwise. +Atk is not recommended for this build without Phantom Spd as his seal, same for +def or +hp variants. +Spd with a spd refine gets Niles up to 39 speed, fully merged 43, and through Speed Ploy he can bring any unit at 43 speed (47 full merge) down enough for Flashing Blade to trigger. Felicia may be faster and has more res, but will usually die when Niles baits her providing she does not run Windsweep, so he does not need to worry about not being able to Ploy her.
For baiting purposes, assuming Niles can double naturally or through Quick Riposte (and his speed is still higher, even marginally), this build functions identically to Killer/Slaying Bow with Distant Defense in the A slot. Even when initiating, little difference may be seen from enemies who can counter. The real difference comes when he initiates against things he one shots or enemies that do not counter: free extra special charges he otherwise would need to spend more turns gaining. So long as he is fast enough to double, 4 CD Glacies is effectively cooled down at the same rate as Killer/Slaying Bow 2 CD Iceberg. Flashing Blade also neutralizes Guard, allowing Niles's cooldown to decrease at a normal rate instead of being stopped or slowed.
Glacies is recommended over Iceberg solely for the power output, though Iceberg is certainly still usable. Aether can also be considered if the user wants something higher scoring for Arena. Despite its 5 turn CD, it can still be fully charged in a single round where he can double and is faster, allowing it to be used right away in the next matchup he enters.
Guard is an option for his B skill to punish the special charge of his enemies while he reaps the rewards of speedy cooldowns, though Quick Riposte is higher scoring for Arena and can still allow Niles to usually double against Bowbreaker units. Spd Ploy is a must with this build to allow Niles to outspeed his targets, especially if the opposing team is running Chill Spd or Gunnthra with her default Chilling Seal. Spd Smoke is an alternative to Spd Ploy, especially for -res Niles that want to be more sure of debuffing the enemy, or simply just wanting more area of effect.
For his seal, Distant Def stacks with Guard Bow for +12 to his def and res when baiting ranged units. Phantom Spd can be used as an alternative for less bulk in exchange for virtually adding +10 to his speed stat to more likely ensure Flashing Blade triggers. Phantom Spd can also allow Niles's C skill to be more open to alternative skills like other Ploys or supporting skills.
His Assist skill is entirely dependent on the needs of the team he is on. Draw Back, Swap, and Reposition are all useful skills to put him or his allies in better positions. Dual Rallies like Rally Def/Res score more points for Arena and are the most recommended for a full arena build. Avoid Ardent Sacrifice when running skills depending on having high HP thresholds, like Quick Riposte or Guard, thought AS paired with Renewal turns this build into something better for Tempest Trials or Chain Challenge modes.
This build loves dancer, Infantry Pulse, and/or speed support. More speed means more opportunities for Niles to quickly charge his special, which means any Rally, Hone, Spur, or Drive skill to increase it synergizes well. Any speed-boosting Legendary Hero on the same team during the appropriate element week will make great allies for Niles. Infantry Pulse is yet another means to charge it faster, and even a single Pulse will mean Niles can Glacies nuke a ranged unit he baits in a single round through either doubling or Quick Riposte. Dancer support is excellent for letting Niles move again after charging his special through baiting or attacking an enemy that cannot counter, then using his nuking power on an enemy that otherwise wouldn't take much damage.
Overall, this build makes itself more situational and reliant on speed, making it slightly less universal, but potentially more powerful in terms of frequent special output. Despite its expensive skills, it can be a high reward build for those wanting to capitalize on Niles's assets.