Stage 1: The Newbie (Developing 1* Roster)
Overview:
Get to the last 2 stages of prologue while spending as little iso on your 1*s as possible. I think my main team was all around level 30 and I had completed most of the prologue before I made the next stage, so that is probably a good benchmark to go for. This has recently become a lot harder since the amount of 2* covers given out as PvP rewards has been drastically reduced, so level your 1*s up to max level if it looks like it'll take a very long time to get enough 2* covers. Focus on leveling up your core team such that it is strong enough to complete most levels in the prologue. Also poke around in the current PvP/PvE tournaments that are going on: while you won't get terribly far, they do offer a ton of standard tokens and iso for you to get. If you can, aim for the 300 point progression reward as that will get you a guaranteed 2* cover. Opening any tournament at the very beginning will match you up against seed teams, which your team should be able to easily beat for points. I wouldn't recommend actually joining the tournament and playing your first match until later though, since your bracket will be much tougher as the only people who join right away are hardcore people.
Tips:
ONLY spend HP on roster slots. As you go further into the game, you?re going to be getting new heroes at a rate much faster than you can acquire HP, so do not spend any HP on anything except roster slots. Every character will be useful eventually due to particular PvE/PvP events requiring specific characters, so try to have as much on hand so that you can use them when the need arises.
Feel free to sell off any 1* covers that you haven't put much ISO into (level 10 and under) if you need the roster space. These covers will be plentiful later and tend not to be particularly useful in general. In order, sell Yelena, Venom, Juggernaut, and Hawkeye as needed.
When you're running low on health, use health packs, as they regenerate over time. If you're out of health packs, swapping in your B team (such as Juggernaut for IM35) will let you play longer if needed.
If you run out of roster space, consider saving up your standard/heroic tokens. If you open up a new character with a full roster, you won't have the space to use it, so you can stash them until you have space. If you're cover starved though (in that you have your characters at max level and need more covers), you should probably just bite the bullet and use up the tokens.
Don't complete the missions that give you 2* covers until you already have 3ish of those covers obtained elsewhere. 2* characters with a small amount of covers are just going to be wasted roster space as they'll be vastly inferior to your 1* covers, so you might as well wait until you can actually level up the 2* covers to a reasonable level before winning the guaranteed ones in the prologue to conserve some extra roster space.
Also don't repeat Prologue missions that have 1* covers you do not need (Venom, hawkeye, etc). Later in the game if you want those characters, those missions will be super easy and will be a reliable source for those covers. Same goes for boosts and health packs that you probably don't need at the time: you can save them for when you need them (like a PvP session), and beat the mission then.
If you run out of roster space, sell Yelena, then Venom, then Juggernaut, then Hawkeye. You'll be able to get a ton of standard tokens in the future to rebuild these characters if you want to, so don't worry about having to get back the covers. In general, once you stop using a 1* character, you'll probably stop using them forever. The only time where they are actually useful are during random PvP tournaments where only 1* characters are allowed, but this has only occurred twice in the history of the game, so don't expect them to be useful that frequently.
The Lightning Rounds are the best source of iso in the game: join at the very beginning (opening minutes) of each one, and you'll see weak seed teams that you can easily beat. You get a standard token and a good amount of iso for going up to 100 progression points which you can do off of seed teams, so do as many as you can to farm iso. Your team isn't strong enough to compete in them yet though, so I wouldn't go for much more than that.
Key Characters:
Juggernaut - A very strong tank and PvP character. Unstoppable crash and headbutt are extremely efficient at 5/5 as they only require 2 matches to activate. His main downsides are that he isn't as sustainable as other characters due to headbutt costing hp, and by the time you get enough of his covers, you probably already invested a lot into IM35, who fills the same role as him. However, his red / green only costing 6 AP means that he's a lot faster/scarier than IM35, which actually makes him significantly better at this stage in the game. If you are reading this guide and don't have your IM35 past say level 40, spending iso on leveling juggs will probably give you a much easier time as you transition into 2* land. Another small downside is that you can't use Juggs in prologue nodes involving Juggs, so keep your IM35 for those.
IM35 ? Your first tank and main source of damage at the 1* stage. His red does solid damage for a 1*, his yellow provides nice utility and a secondary source of damage, and his blue will never be used due to how expensive it is, but packs a punch if you can get it off. A solid character for transitioning into bigger and better things.
Ideal Build: 5/5/3 ? Again, you simply won?t have the AP to case blue a significant amount of the time for it to make a difference.
M. Storm ? An amazing board clearing / AP generation character even during the later stages of the game. Her yellow generates TU AP/cascades, her green generates a ton of real AP/cascades, and black is a decent source of incidental damage early on.
Ideal Build ? 5/5/3. While hailstorm is tempting for the damage, I think M. Storm's AP generation/board clear capabilities are more important, so you?ll want to max out yellow/green. 3/5/5 if you're running Juggs since you're never using M. Storm's green over Juggs green.
Modern Black Widow - A fine utility character for stealing AP and chain stunning enemies. Her stun helps greatly in making sure that you can prevent pesky countdown tiles from activating in the Prologue. Note that since none of her abilities deal damage, she doesn't scale well with leveling, so only level her up enough to survive pesky AoE attacks.
Ideal Build - 2/5 - It may seem wrong to purposefully not give a character covers, but Black Widow's purple ability is actually much faster at lower levels. The benefits of stealing black AP (fueling hailstorm which isn't terribly necessary), getting 4 AP per steal (enemy matches only generate 3 AP so 4 AP is harder to get), and purple AP isn't worth the extra AP that the ability costs at higher levels. Keeping it at two allows you to steal the more important colors (Yellow,Blue,Red,Green) for your team and keeps the ability at 12AP, which is 4 purple matches.
Classic Hawkeye - A utility character meant for board clearing/control, but is overshadowed by M. Storm in almost every way.
Ideal Build: 5/5
Character/Team Compositions
Juggs/M.Storm/M. Black Widow ? Probably the best, most cost effective team for this period. Juggs covers red/green with strong, offensive abilities, M. BW gets blue/purple, and C. Storm has yellow/black. Juggs also costs less iso to level since his cap is 40, and M. BW being at 2/5 means a lower level cap as well.
IM35/M.Storm/M. Black Widow ? The cookie cutter team comp for someone who is just starting out. Covers all colors while having strong abilities in all of them. IM35 is the main damage dealer/tank, M. Storm clears the board when needed, and M. Black Widow provides AP stealing / stun support. In this team composition, always keep Iron Man at least 1 level above Storm and at least 7 levels above Black Widow. This will allow him to have higher tile match damage than M. Storm and Widow in the colors they share, and thus allow him to be at the front and tank all of the damage, which means that you can conserve health packs by only healing him.