Alliance Takeover (Defend Your Zone/Alliance Vs PVE)

zodiac339

On the PVE side of Versus events, a Capture and Defend event could be an interesting experiment. Making it a hybrid PVE/PVP opens up fascinating options for what players could do.
Event Resources: Completing missions, successful defenses, and even losses (via salvage) could generate special resources and/or currency to strengthen your defense.
Defense Boosts: Through resource use, you could give your defending team an edge with AP and Match Damage Boosts.
Mercenaries: Have you ever thought to yourself, "Why can't I abuse minion AP generation?" Well, why not hire some minions then? While the developers may not allow you to use minions on attack, sad if it wasn't allowed, but probably necessary for the occasions when your heroes die and you stop being able to make matches. Instead, like boosts, you buy them for your defensive team. Cost needs to be appropriately weighted to the minion, with fragile Doombots being cheap, Magia Muscle being much stronger and more costly than other Magia types, Symbiotes as a whole being expensive (except Destroyers), and maybe just leave out the Ultron Sentries?
Choosing your defensive team: The default on a defense is normally the team that you used. Spending resources opens the possibility of spending to replace members, not just with aforementioned mercenaries, but potentially with members of your roster that you didn't use or with Alliance provided heroes, in a similar fasion to sending team ups; every member of the alliance provides at least 1 hero, perhaps 2 if the pool were as large as 40.
Alliance Headquarters: A big mission, designed to only be attacked a limited number of times. Other missions would have to be completed in order to open this one up, and it would close like a boss fight until other missions were completed again. Worth the most points, and truly an Alliance defense, this would be set up by a commander as a wave mission using heroes from the alliance pool of heroes.
Scaling: The ability to use alliance provided heroes, as well as a player likely having uneven levels even within a given tier, makes scaling the defending team an important aspect. Additionally, very few alliances are made up of players with the same roster levels. Matchmaking being what it is, Alliances could be pitted against one another with vastly different levels of power, basically having the system pitting them against each other and predetermining a winner if there isn't scaling. Therefore, an appropriate scaling system would be required.
Phases: An event couldn't simply start and go "Okay, you two are fighting. Go!" as that could lead to a dead alliance against an active one. Instead, there would need to be a Seed Phase of at least one, and potentially three days. During this time, Alliances would be playing the more classic style of PVE, hitting missions to generate resources (and claim territory?). There would be an intra alliance competition at this point to determine who actually gets to set the initial defenses, and which commander (if more than 1) sets the Headquarters defense. After that, Alliances get matchmade against one another. Individual missions should have the names of the players assigned to its defense. If there are boosts, those should be listed in place of team ups. The wave mission of the Headquarters should be viewable so that the attacker can see exactly what they're in for, especially since the mission is super variable compared to normal PVE.

This might be a difficult idea to pull off, especially if a 1 v 1 would leave an odd alliance out. Alliance groups might be necessary. The whole event could take 4 days to a week to go through.
Oh, also?
No boosted heroes: Instead of typical scaling that can go 40~50 levels above your roster average, the highest scaling would be at your average and not provide any boosted heroes to blow through it. There could still be an easier set of mission (assigned to alliance members who didn't do as well during Seed Phase) that would allow Epic players to use Legendary and Rare heroes.

zodiac339

Additional thoughts:
Seed Phase, then Build Phase (1 day, once intra-alliance placement is determined), then Battle Phase.
Headquarters Assault is like a boss battle. The top 3 to 5 players are assigned to the missions that unlock the Assault during the course of a reset period. Consider a reset period of 24 hours instead of 8.
Members below top 3/5 are assigned to repeatable missions that could provide additional resources, but are mainly there to provide alliance points along with additional player engagement and minimize the loss of ISO and other personal resources that are normally lost during an alliance event.
Thinking of it as an alternative to a Boss event, the Battle Phase could be set with a progress reward structure rather than going for a system of alliance placement. This would open up the matchmaking system to avoiding "odd alliance out" situations, and instead, only putting alliances with enough members and engagement into a pool of "defending" alliances for other alliances to attack. Then, alliances short on members could still participate in the Battle Phase, even though they don't have adequate members to defend. Working with a pool of defending alliances also opens up the ability to fight a new alliance each day.
If alliance placement was desired, that could still be included for the Seed Phase, based on which alliance generated the most resources during that phase. Thus, any given PVE could potentially be assigned as the Seed Phase, with the points being considered resources during the Build Phase. (Probably better to have a unique map though to really give the feel of taking over territory)