If one interests you, or feels like something the character could do, try to adapt it into a loyalty ability (or even a static!) Dont feel bad if you end up with a classic planeswalker design (5-mana, 4 or 5 starting loyalty, +1 card advantage, -2 to 3 removal, -7 or -8 ult that has the potential to win the game if you can back it up.) This design, and other often seen designs, are classics for a reason: They work
Some have come and gone, while others, like EDH, otherwise known as Commander, have become such a force that they've dictated the release of entire sets dedicated to the format
14 Kelsien, The Plague Starting off as a 3/3 Assassin, Kelsien, the Plague gets +1/+1 for each experience counter you have
I'm unsure how good the Seek Thrill portion of the card is, considering you mill over the cards, and they go to your hand
If you control three or more creatures, it gets +4/+4 until end of turn instead