The elder gods are the most powerful, as they are tier 1. Jas is the strongest, then Wen, Ful, Bik, and Mah (by age). As for the 5th elder god, I'm not sure.
The next strongest in line are probably Seren and Zaros, as they were both born from Elder Gods. They are considered tier 2 transcendal gods. Whether Zaros is more stronger than Seren or vice-versa, we do not know yet. Seren has a closer spiritual-divine bond with nature and the soul of Gielinor, giving her lots of power. Zaros never showed a close divine control over the anima like Seren, which suggesr he could be weaker. He was also just resurrected from scratch, having to live off of her mom's dreams like a baby weening. Seren was still connected to the whole anima ecosystem of Gielinor while she was shattered...
As for the strongest god not born from elder gods, Guthix is the strongest. Is Guthix stronger than Seren and Zaros? We do not know. I don't think he is, since he was taught by Seren how to connect with the anima mundi and ascend to tier 2. Guthix is dead now, so he is irrelevant now.
Saradomin is tier 3, and is the strongest of the nonelder borne gods. He has still yet to find the secrets to ascend to tier 2.
No god is invincible, however. Any elder weapon, like the Staff of Armadyl, can easily slay any tier 2-5 god.
I worship Mah, for she is mah homegirl! The correct adjective for Mah's followers are: Mahomies, Mah-homeboys, or Mah-homegirls.
27-Aug-2016 22:25:56