Ecutioner is a "Single target" unit, his main role is to eliminate units with low health.
Passive: Death Sign
Insta kill if unit health fall below % of max health
Active: Death Call
Execute units with low hp
Tactics: passive - this passive goes really well with units such as "Blaze" that can get the enemy units to low health and apply execution on them, Another good use it to Execute units with "low %" of health but with high armor such as "Golem".
active - "Death Call" is extreamly powerfull as it can help clearing multiple units from the field, "freeing" your turrets to focus on more quality targets. work on the timing as its crucial with this skill.