5star Thanos cover = instant delete?

I think you will get a lot of differing opinions, and the answer may partly depend on several factors, such as whether you are a casual or aggressive player, and how much money you are planning on spending on the game.

If you are an aggressive player and / or spend a lot on the game, then you will probable advance your roster quite quickly, and having this 1 cover white elephant 5* might not be a big problem.

On the other hand, if you are a casual player, and either plan to play for free, or spend a minimal amount, you might be better served to get rid of this cover, as painful as it sounds & feels.

Your scaling is calculated at the beginning of each regular PvE / PvP, so at least keep the cover until after the start of the next regular PvE event & see if, or how badly it messes up your scaling. With the new scaling system introduced in early fall 2016, the effects of a low level roster accidentally acquiring a 5* or two have been reduced, but (in my opinion) not completely mitigated. If, after playing a few nodes in your next PvE event, it feels like the difficulty level has significantly increased, then you should probably consider selling the 5* cover. If you feel little, or no difference, then it won't hurt to keep it. Keep in mind that when a 5* makes a match 3 in it's primary colors, the match 3 damage is typically in the range of 300 to 400 points, and this can be a real bonus if you start playing seed teams in the Lightning Rounds - just the match 3 / match 4 damage from a 5* helps wipe them out in no time. (Check out the topic "Mining ISO-8 from Lightning Rounds" on these forums if you haven't already!! https://d3go.com/forums/viewtopic.php?f=6&t=29586&hilit=mining+iso+from+lightning)

I've been playing casually for a year, and the best advice I ever received was after joining a new alliance last July. Our top two, highly advanced players both told me to "not even think about opening or buying any Legendary Tokens until your roster is much more advanced". So I have a stockpile of LT's awaiting the day when (possibly) acquiring some more 5*s makes sense.

I realize this is a special case, you probably got this from winning something in the current special events, so it's unfortunate... my winning pulls have all been 4* so far, and hopefully will remain that way.