Spellcasting. The abjurant champion is a 7th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 12, +4 to hit with spell attacks). The abjurant champion has mage armour constantly active and can cast it as a bonus action or a reaction if targeted by an attack, and has the following wizard spells prepared:
Cantrips (at will): blade ward, fire bolt, shocking grasp, true strike
1st level (4 slots): mage armour*, magic missile
2nd level (3 slots): misty step
3rd level (3 slots): counterspell, dispel magic
4th level (1 slot): stoneskin
* the abjurant champion has already cast this spell on itself before combat

Longsword. Melee weapon attack: +4 to hit, reach 5ft., one target. Hit: 5 (1d8+1) slashing damage. When the abjurant champion hits a creature with a melee weapon attack, it can expend one of its spell slots to deal force damage to the target. The extra damage is equal to 2d6 for a 1st-level spell slot, plus 1d6 for each spell level higher than 1st.

Enter the description for how bonus actions work for your monster here.

Abjurant Armour. As a reaction when an opponent targets the abjurant champion or an adjacent ally with a weapon attack, the abjurant champion magically increases the target's AC by 2. This ability may be used twice.