Allison was not much help to her father in The Umbrella Academy season 3 finale, making it even more confusing why Reginald made a deal with Number Three. The origins and motivations of Reginald Hargreeves have been some of the biggest lingering questions for The Umbrella Academy. Season 3 finally peeled back the curtain to reveal more about what he wanted to accomplish, as his super-powered children were a ploy to help him reset the universe. It is only in a new timeline where the Sparrow Academy and Umbrella Academy meet that Reginald is finally successful, and it comes after he makes a deal with Allison to help him.
Reginald Hargreeves' interest in resetting the universe did not sit well with the rest of the Umbrella Academy, but Allison understood that this was the best way she could regain the life she lost after traveling through time again. The Umbrella Academy season 3 focused on Allison's pain after no longer having her husband and daughter. It resulted in some controversial decisions for Number Three, such as forcing Luther to kiss her, but making a deal with Reginald also alienated her from her siblings. The Umbrella Academy season 3 finale shows that it worked in Allison's favor as she is reunited with her family.
While Allison and Reginald's deal makes sense from her perspective, The Umbrella Academy season 3 never explains why he would do it. Reginald has more knowledge of what is going on than anyone else, and he makes a deal with Allison hoping she could convince her siblings to follow his lead. Even though she fails to do this, Reginald secretly kills Luther to convince his children to do what he says. His plan goes perfectly from this point forward, with the only trouble coming when Allison has a momentary change of heart and kills him. Since Allison ultimately resets the universe with Hotel Oblivion, even that decision is somewhat meaningless. Reginald and Allison's deal would have made sense if she was going to use her "I heard a rumor" powers to force them to follow their dad. Without such a move, The Umbrella Academy season 3's deal does not seem like a logical move for Reginald.
Why Reginald Might Still Need Allison In Umbrella Academy Season 4
It is possible that Reginald's deal with Allison could be about what is to come in The Umbrella Academy season 4. He purposefully stops Allison from stepping on one of Hotel Oblivion's 7 stars, which drained the power from all of her siblings who did just that. While Reginald could not have accounted for Klaus' returning from the void, his decision to spare Allison from the effects of Hotel Oblivion is noteworthy. So is the fact that she is the only one who gets a happy ending in The Umbrella Academy season 3. It is possible that Reginald knows he will need Allison's help (and powers) moving forward to keep the reset universe intact.
If Allison is part of Reginald's bigger plans for the universe, all eyes will be on what that entails and if Allison agrees to follow her father's schemes to preserve the life she has with her family. She could be positioned to become an even bigger villain in The Umbrella Academy season 4. There is also the chance for redemption. Allison could see the Hargreeves empire she helped create for her father and learn of how he is misusing his power, along with stripping away the powers of the other Umbrella Academy members. Turning against him to help save her siblings could redeem Allison's The Umbrella Academy story.