Pro tip: Only grade near-mint or better cards to avoid losing money on grading fees
People love building around Sundial of the Infinite, and Time Stop is a super-powerful and popular effect in Commander because it can fizzle opponents mid-combo or mid-attack
Giving your team hexproof is a great roadblock for your opponents since they need two pieces of interaction to kill anything that's not Sigarda, but the card advantage is what you want
It doesnt do anything else, just blows up the battlefield, leaving it clear for you to rebuild or for you to drop a planeswalker or two on your next turn
Force an attack Another way blue can deal with a creature is to force it to attack into something that will block and kill it
In general, I would look at these two factors when looking to include cards not of your tribe's creature type: Is this creature so strong that it, on its own, is generally stronger than my tribal creatures when they are receiving bonuses and/or empowering my other cards