I will just start by saying the reason jiyva is not in temple or a starting option is because it is a "anti-crawling" god - Jiyva eats the loot in the dungeon that the player is supposed to use to strategise a way to survive through the game, then gift mutations that replace equipament slots(such as resistances, AC from scales and so on). Now lets head for the quotes:
wisp412 wrote:I was thinking that a Jiyva fighter as a starting class would be fun.
It would be fun for like the first few times you played it, then you realise how utterly broken it would be. What makes a early jiyva run fun is how rare it is to get one, jiyva is not that fun on itself if you look deeper into it. If you think the mutation ride alone is a fun factor there is Xom for you.
Croases wrote:a player wanting to worship it early on can scum for slime temple, so there's no real reason not to put a Jiyva altar somewhere in the early dungeon.
I have only seem slime temple like 4 or 5 times on the 4000 times i played this game, so i doubt that. There are other early jiyva temples you can find, but goodluck start scumming those. It is much easier to just take a dive to lair and hope for the best, but then its not early anymore anyways.