Ladies and Gentlemen: let me introduce you, to the best ally in the game
There are two main ways you lose in Arkham Horror LCG: either the encounter deck defeats you or you run out of time when the doomsday clock hits noon.
You mainly lose by time out because you wasted or did not have enough actions to complete the scenario.
And one of the main actions that consume the lion share of the limited amount you have every scenario is the dreaded concept of moving
That is why Shortcut is considered such an incredible card that is a mainstay in any seeker deck: spending a card (and no action, mind you) moving is considered INCREDIBLY powerful (especially because the level 0 version of shortcut also does not cause attacks of opportunity, allowing you to safely "drag" an enemy away, something that is not true for the level 2 version which, between that and the added cost of 1 resource, is significantly less popular) [Edit: People in the comments pointed out there is a difference between "taking" an action and "performing" an action: you always perform an action when you take it unless it is somehow nullified ot stopped, but you don't always need to take an action to perform it. Shortcut lv2 is an example of that, and Attacks of Opportunity care if you "take" an action, even if you are not spending actual actions to do it. If you perform the action, you do not get attacked, so the upgraded shortcut won't cause you to get smacked. You will STILL lose an action from Frozen in Fear however because it will trigger every time you perform an action at all, while base level Shortcut and Allegria do not make your perform a move action, they move you as an "effect"]
Enter Allegria: who for the admitedly high price of 4 resources (though for an ally it's quite a baseline cost). gives you a soak of 2/2 and the ability to move every round to a connecting location without spending an action, and said movement also does not provoke attacks of opportunity
That is asbsolutely bonkers good and unbelieveably versatile: you have an enemy on you and another one about to punch you in a connecting location with the hunter keyword? Just either move away from the hunter or engage him too if you can defeat both,
Got teleported one the other side of the map? Slowly crawl back there one move per turn as you do other stuff on the way or get immediately there with 4 moves
Need to do one last thing before resigning and only have 1 extra round to spare? That would usually leave you with 2 actions, 1 to move to the location you need to be to do what you need to do (if it is in a connecting location), another action to do it and one to move back and then going through the mythos phase before you can resign (Chuck Fergus shennanigans with "I'm outta here!", other types of free movements and extra actions not withstanding), with Abess? You can actually do that in one round!
That alone would be enough to make Allegria one of the best allies in the game sought by all classes but maybe Seeker who have a decent alternative that is cheaper in resoruces, does not occupy and ally slot but is not as versatile in return, she doesn't need anything else to be fairly broken on its own: and yet she does have another ability that comes up in multiplayer...
She is one of the few allies other investigator can use the ability of, even if they are not at her location (as long as they are in a connecting location.
Specifically Allegria can "push" another investigator out of her location or act as a rope and drag that investigator in the location the one controlling her is, as long as the moving investigator is in a connecting location
That is nothing short of amazing: this nun does not make it harder just for you to lose by running out of time, it also helps others with that. There are only few allies that are as versatile as Allegria in that regard, and most of those I can think of are just meat shields that can tank damage and horror for other investigator beside the one controlling them
I am not joking when I there is not investigator that doesn't want Allegria: Guardians can close the gap faster to reach enemies and lay the smackdown, Seeker can stack Pathfinder and get to place with clues at insane speed, Rogues get to evade an enemy and move away immediately (which is usually as good as killing them if they are not hunters), Mystics can drag themselves away from danger if they are not ready to face a threat and Survivor... Can do what Survivor usually do and get a free actionless move every turn I guess
The way Allegria synergises with every investigator goes from complementing them perfectly (Roland can beat up an enemy on a location with clues after Allegria helps him drag them there, Luke gets esentially a free Elusive that brings him to his Dream-Gate and Monterey Jack can cash out with his signature ability without even spending an action. Keep in mind all these investigator can also take Shortcut and Pathfinder to be able to get from one side of the map to the other in one turn without spending an action easily) to not synergising with them really, but allowing every single one of them to do what they do spending one less action moving every turn
While Allegria support is brilliant in multiplayer, I think where she truly shines is in single: this Nun singlehandely might make it possible for true solo investigator to not just get through the campaign, but actually win most scenarios, especially those with massive maps like in Innsmouth Cospiracy and Edge of the Earth
Althought I do have to admit: I might be a bit biased here. As an Italian man I am very proud to regard an Italian nun be one of the best cards in the game in my experience playing her.
Beata tu sia suora Allegria de Biase: sei veramente la più benedetta!