For cards/abilities that say 'any number of units' (like Volibear Furious or Foxfire), can you choose 0 targets?

Ruling: No, you cannot choose 0 targets for abilities that say "any number of units." These abilities require at least one legal target to be put on the chain.

Sequence:

• When an ability that targets is triggered, it must have legal targets to enter the chain
• If no legal targets exist when the ability would trigger, it does not enter the chain
• If legal targets exist, you must choose at least one target (minimum of 1)
• The ability then resolves with those chosen targets

Nuances:

• For damage-dealing effects like "deal 5 damage split among any number of units," the damage must be dealt to something - you cannot deal damage to nothing, which requires at least one target
• For effects like Foxfire that target "any number" of units, you need legal targets to cast the spell in the first place
• Card text saying "any number" does not include 0 because the action (dealing damage, killing, etc.) requires at least one valid target to be performed