The Illrigger has two core ability categories: martial offense and infernal power.

Strength

Strength is appropriate for heavy melee weapons and Strength-based martial builds.

It supports attack rolls, damage, Athletics, and several front-line concepts.

Dexterity

Dexterity supports finesse and ranged weapons, initiative, Dexterity saves, and Armor Class in lighter armor.

A mobile or ranged Illrigger often prefers Dexterity.

Charisma

Charisma is the class's infernal ability.

The Interdict save DC uses Charisma, and Contracts can use it for spellcasting or other effects.

Some Combat Mastery options also allow Charisma to become part of the character's weapon or defensive plan.

That makes Charisma more important than a normal secondary social score.

Constitution

Constitution supports hit points on top of the d10 Hit Die.

It is also one of the class's saving throw proficiencies.

A front-line Illrigger or a character using risky vitality-transfer features benefits from solid Constitution.

Multiclassing

The Revised Illrigger requires:

Charisma 13 and Strength 13 OR Dexterity 13

for multiclassing under its rules.

Practical priority

Typical martial Illrigger:

Strength or Dexterity → Charisma → Constitution → remaining abilities

A Charisma-heavy Combat Mastery or Contract may justify raising Charisma first.