Who goes first in a card game? Usually, that choice starts off with a simple coin flip and goes back and forth after that. And while in Artifact the game starts with a coin flip too, afterwards it’s up to the players to decide who gets to make the opening move at the start of a turn — i.e. who has initiative?
Initiative is all about the action phase. The player with initiative starts off by playing a card or triggering an ability, then the opponent can do the same. This goes back and forth until both players pass their turn. But if you play a card that reads ‘get initiative’, that means you can take another action immediately, without your opponent’s interference. You can also get initiative and pass your turn — this means you will get initiative in the next lane.
Two heroes’ premier cards boast this powerful effect. Tidehunter’s spell is as cheap as they come and gives a nice little boost. Its power lies in that cheapness though — you can use it to squeeze in initiative at the very end of the action phase and set up a strong start in your next lane. Chain Frost — Lich’s signature spell — has a far more significant impact on the board, and its cost reflects that.