Getting 5 wins in casual isn't really that hard. The hard part is just finding a match as Casual Match is 8 or more people in a lobby and 2 people fight while the 6 spectate the fight. The winner stays and the next person rotates in which means it could take forever for you to get in a match and if you lose the match, its back to waiting.
My suggestion is to create your own room and make the room policy Beginner's room since I found people at the same level as me and I'm one level above the starting level (the sprout icon.) Once someone joins your lobby, start up the match. I played as Nightmare to get my 5 wins and he is a BEAST imo with his long range and power. If you win, you stay. If you lose, you are put back into the rotation but most times, it's just two people in the lobby so you can just fight your opponent again. If there are more than 2 people in the lobby, just back out and create another lobby.
Hope this helps!