If the Chrono Legionnaire is killed while erasing a unit, the partially-erased unit will reappear.
While being erased, the enemy unit is invulnerable. The more powerful the enemy, the longer this takes. Rather than destroying enemy units and structures, his weapon simply erases them out of time. While phasing back in, the Chrono Legionnaire is vulnerable to enemy fire. The distance of the teleport determines how long it takes him to “phase back in” at his new location.
Instead of walking, he teleports around the map. A Chrono Legionnaire never walks anywhere.