I've seen Halfling reroll used - kobold hit him with an 18. "Halfling second chance!" - reroll gets a 20! The halfling dodged into a critical hit![]()
You don't use the halfling power to just dodge a normal hit. You use it to dodge the crit, then if the monster still hits you, you've at least avoided the max damage.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.