Can I use animate characters in an iOS game if I do a citation in the credits. Ex Steven univers in a fighting game and I list Rebecca Sugar in the Credits or by the character bio.
While the details of copyright law varies by jurisdiction (US versus Europe for example), the general thrust is basically the same: copyright gives the author of the work the control over who can use the work and how. It is only okay to use somebody's copywritten work if they have explicitly permitted you to do so.
"Giving the author credit" or "not making a profit" do not exempt you from copyright law.
The one real exception is "fair use" doctrine, which permits certain usages under certain very specific and limited scenarios. You're game almost certainly does not fit the criteria.
You should always consult a lawyer for legal matters such as these. If you feel like you "cannot afford" a lawyer then you absolutely should not be trying to skirt copyright law because getting sued or suffering a cease-and-desist is far more expensive or impactful.
Use your own imagination. Make your own games.