In 13th Age, like most D20 variants, you can have items or abilities that improve your crit range. However, in 13th Age, a natural 20 is a automatic crit hit (if I am not mistaken, you do not need to check if you hit). What is unclear to me if say I have +2 Crit Range (18-20), is it an automatic hit if I roll a 18, or do I is that just a threat and I need to roll to see if I hit?
Updated with the rules (pg 196 of the Escalation V6 version)
Every attack roll that is a natural 20 is a crit ('critical hit') for double damage.
And that's all it says. Here's the part on crit range:
Each point of improvement in crit range drops the number needed to score a critical hit by 1.