Tolarians teach the theory of pyromancy. The Ghitu prefer applied research.

Ghitu Lavarunner

As long as there are two or more instant and/or sorcery cards in your graveyard, this creature gets +1/+0 and has haste. (It can attack and {T} as soon as it comes under your control.)

Foundations

The List

Dominaria

As long as there are two or more instant and/or sorcery cards in your graveyard, Ghitu Lavarunner gets +1/+0 and has haste.

If Ghitu Lavarunner loses haste after being declared as an attacker on the turn it comes under your control, it will continue to attack. It won't be removed from combat. On the other hand, if it loses haste before your declare attackers step, it won't be able to attack.