Holdout Settlement
Oracle Text
: Add . ( represents colorless mana.)
, Tap an untapped creature you control: Add one mana of any color.
Card Rulings
1/22/2016 To activate the last ability, you may tap any untapped creature you control, including one you haven’t controlled continuously since the beginning of your most recent turn. (Note that tapping the creature doesn’t use [the tap symbol].)
Many decks have creatures that are there for abilities and not attacking or blocking. Like blood artist for example. Taping that creature is of no loss at all.
I could see some fun with the untap mechanic from shadowmoor and eventide.
Its a way of preventing a "this creature must attack if able" creature from attacking.
5 color creature decks are difficult to build. You either have to spend a fortune on things like Cavern of souls which only helps if your deck has a shared creature type. Or things with harsh downsides like city of brass, ancient ziggurat, pillar of the paruns thran quarry or gemstone mine
In my opinion in the right deck this card's downside will hardly even be noticed.
With so many nonbasic lands that produce the new colorless mana one does wonder what the point of the wastes is