Through the use of cards like Back to Basics and Rising Waters, Urza can greatly limit opponents' mana access while still being able to produce mana for its controller through the use of artifacts
The one that got the biggest consideration from me was Auspicious Starrix, because getting it once was enough
Therefore, I recommend that most Spellslinger decks contain some form of combo, even if its just a four-card combo with no tutors
maybe gain infinite life along the way
As such, it lends itself very well to deck upgrades, but even if you forgo upgrading it, Limit Break is still a great deck to play with out of the box without any alterations
There are plenty of different ways to take advantage of unblockable creatures, from loading them up with equipment, to enjoying free Ninjitsu triggers in your Ninjas deck