Ok, I've won with Jiyva for a 15 tournaments run and a DsGl. It wasn't so hard, actually.
A few advices for anyone who never tried Jiyva before, and wants to.
1 : The safest way is not to pick a god, find a way to go to the nearest Jiyva altar, then go back, do orc completely, then get back to Lair, convert, then come back to D:1 to D:9 and eat EVERYTHING with slimes, then go back to Orc and eat everything (except the gold you already took ^^), then finish the lair. Even if eating a lot of gold will rocket your piety, you need this money, and in Orc you can at least find some useful stuff on monsters (armors, weapons, shields). I didn't take any game because i didn't want to suffer their wrath.
2 : Something very good with this god is that some items can become more useful. Jiyva will change your stats. ALL the time. Trying to adapt (sometimes it's annoying, but, well,...). So, of course, as soon as you decide to play a warrior, you will only find stuff with Int on it. Jiyva doesn't care ! He will change your "Int" in Str. What you have to look is "how much stat" stuff gives. Some items you don't even look otherwise will becomes good. Like my Str+3 Int+4 Dex+3 ring,which gives, actually +10 in "all" stats.
3 : You will loose a LOT of stuff. In my winning game (
https://crawl.xtahua.com/crawl/morgue/Inarius/morgue-Inarius-20180913-100551.txt ), I still had my +2 cloak from the begining. I finally found some good boots, but at the very end (Tomb:2,and Tomb was my last rune). Before that, only +2 boot, thanks to scrolls.
4 : On the other hand, Jiyva specific mutations will gives you some very very very nice mutations. I lost most of them just before the end, but I had for most of Pan rF++ and rC++ mutation. It compensates for most of the crap items, actually.
5 : Jiyva mutations are really great. Acidic saliva is wonderful for quickblades. AND EYEBALLS are just...wonderful. And Tendrills disarm EVERYONE, including pan lords
6 : Last but not least. Consider EVERYTHING as food/hp/mp. You actually gain a lot of time, because after each fighting, you can just spam one jelly which will do the janitor for you, and eat useless weapons/armor/bodies. It will regen your mp/hp very fast, and, basically, you never eat, always engorged...