Wolfteam - How Character Card Upgrades Work
This was performed on one of my twink accounts for testing purposes
Once first card is opened, it's initial level 1 effects come into effect.
As you can see, it required 120,000 gold to make 2nd level upgrade for one blue basic character.
Attention! Character Card stat boosts are permanent and come in effect instantly. you can notice that match starts at default 200 HP, but once you pick a loadout in match, the health boost from cards comes into effect.
Card boosts are impossible to un-equip.
I consider card upgrades an unfair advantage, as they are extremely expensive, requiring millions of gold to max out characters.
Events that reward you cards - are a miniscule drop, and don't fix the issue, I even think that they add to the problem as player is being manipulated to attend in boring events.
My hard advice, is to never open card boxes, never take card boxes from gift boxes, let them disappear in gift box. And if happened to get cards into inventory - just don't open them, and don't upgrade cards.