If it's neither day nor night, it becomes day as Vadrik enters.
Instant and sorcery spells you cast cost less to cast, where X is Vadrik's power.
Whenever day becomes night or night becomes day, put a +1/+1 counter on Vadrik.
Vadrik is an Izzet spellslinger commander who scales his cost reduction off his power, so you grow him and then chain cheap (often free) instants and sorceries. Early turns set up day/night flips and pump effects to inflate Vadrik's power, then you unload a barrage of spells for tempo, card draw, and ultimately a lethal X-spell or copy-storm finish.
Massive cost reduction can make big X-spells and expensive bombs effectively free
Day/night flips passively grow Vadrik and your discount every turn cycle
Naturally synergizes with the deep Izzet spell-copy and draw package
Snowballs hard once power is high, generating explosive single-turn output
Relies on the commander staying alive; lots of value vanishes if Vadrik is removed
Reduction only helps instants/sorceries, not your artifacts/creatures
Vulnerable to graveyard hate and counterspells on key payoff spells
Day/night can be disrupted or be awkward to flip reliably without dedicated cards
Can be slow to come online if power-pumping pieces are missing
Legendary Creature — Human Wizard
less to cast, where X is Vadrik's power.