Each player can't cast more than one spell each turn.

You may cast spells from your hand without paying their mana costs.

When Urdnan, Dromoka Warrior enters, put a +1/+1 counter on target creature.

Whenever you attack, target attacking creature with a +1/+1 counter on it gains first strike until end of turn. If that creature has two or more +1/+1 counters on it, it gains double strike until end of turn instead.