Wisdom remains the spellcasting ability

Spell attacks, save DCs and prepared-spell capacity still use Wisdom. Reaper does not create a new spellcasting ability.

Martial weapons are an option, not an obligation

The Domain gains martial weapon proficiency and later Divine Strike, so weapon combat is supported. A Death Cleric can still rely heavily on cantrips and leveled spells where that is more effective.

Look for paired targets

Reaper and Improved Reaper become more valuable when two enemies are within the required distance of one another. Positioning, forced movement from allies and target selection can therefore matter more than on a conventional Cleric.

Use Touch of Death on meaningful hits

Channel Divinity is limited. Spending Touch of Death on a minor target that was already going to fall may be poor resource use. A boss, dangerous caster or enemy that must be removed immediately is a better candidate.

Remember concentration and action economy

The subclass adds damage tools but does not remove normal Cleric concentration rules. A strong concentration spell can keep producing value while the Cleric uses weapon attacks, cantrips or Channel Divinity on later turns.

Check campaign availability

Because the subclass comes from the DM-facing villainous options in the 2014 Dungeon Master's Guide, player use should be explicit rather than assumed.