Rafaam Curve

Rafaam curve is named after the minion-stealing Rafaam: its goal is to use 1 cost heropowers every turn in the earlygame for maximum utility, while picking up useful tier 1 minions (similar to warrior curve). Rafaam curve levels to tier 2 on turn 4 (6 gold), to be able to heropower every turn without wasting gold.

Rafaam curve is strong on heroes with 1 cost heropowers that provide value. Examples are Rafaam, Maiev, Mukla, etc.
Heroes with 1 cost heropowers that should not play rafaam curve are those like Toki, Tess, or Saurfang, who do not gain any extra value out of every heropower.

Tribes:
Rafaam curve is not specifically aiming to make use of any specific minion type: since its main goal is to utilize specific heropowers, which tribes are best will depend on the heropower you are using.