Can Warwick split his combat damage to deal 1 damage to 5 different enemy units, or must he assign lethal damage to one unit before moving to the next?

Ruling: Combat damage must be assigned to one unit until it would receive lethal damage before you can assign damage to another unit. You cannot split 1 damage across multiple units.

Sequence:

• Choose the order in which defending units will take damage
• Assign enough damage to the first unit to be lethal (equal to its health)
• Only after assigning lethal damage to one unit can you assign damage to the next unit
• Continue until all combat damage is assigned

Nuances:

• To maximize Warwick's multi-target damage ability, you need to pre-damage enemy units before his attack ability resolves
• Pre-damage can be done by casting spells like Flurry of Blades either before moving Warwick to the battlefield, or after moving him but before his "when I attack" ability resolves
• Warwick's ability triggers during the showdown chain ("when I attack"), not during the combat step, so damage must be dealt before his ability resolves