What type of effect does "Grab the Reins" create when it allows control of a target creature and grants it haste?

"Grab the Reins" creates a control-changing effect because it allows you to take control of a target creature. This effect alters who controls that creature for a specific duration, which is a hallmark of control-changing effects in Magic: The Gathering. Additionally, it grants the creature haste, which is an ability-adding effect. By giving the creature haste, it enables that creature to attack or use activated abilities that require tapping as soon as it comes under your control, enhancing the options available to you for that creature.

Understanding how these effects work helps in recognizing the nuances of the game, such as when a creature can attack or the implications of control dynamics during gameplay. Each of the other options includes effects that don’t apply in this case; for example, while the eternal qualities of a creature might be altered by other spells, "Grab the Reins" does not change the creature's type or set its power and toughness, nor does it involve type-changing effects. Thus, the answer combines the correct aspects of control dynamics and ability enhancements that occur with this card's effect.