A very decent guide. I really like Jungle-Leona. +1
Here are some thoughts on how to improve it:

• - since jungle creeps have no MR, you better take Greater Mark of Attack Speed or Greater Mark of Attack Damage, every bit you gain in damage counts.
• - this brings you to 10% CDR together with Sorcery and allows you to clear 10% faster. Just grab an early Null-Magic Mantle.
• - As an alternative this item is very underused, but Leona does really need the cheap HP, plus team support.
• - you should include this item in your situational items.
• - no matter how high your AP, AD or AS is, you will always need at least two ability rotations to clear a camp (13 sec without CDR, 7.5 sec with 30%). To speed up your jungle time, early CDR is paramount, you need it around 10 min, not after a difficult 25 minute failed early game. I also don't think she needs Mercury's Treads since any CC will most likely only affect her after she used her combo and is waiting for her skill CD anyway.
• - Leona doesn't provit from Resistances as much as other tanks do, seeing that her Eclipse gives her huge resist buff. HP is the way to go for early tankyness, Glacial Shround gives her no HP its better for tanks that need resist, at least early game, late game its pretty decent, but Randuin's Omen is better since you will have all the CDR you need already.
• - I consider maxing this over Shield of Daybreak since you need all the AOE damage you have for faster clear time. But It is even possible to start with this if you get a nice help on wolves and pull on blue, allowing for even better lvl 2 ganks. If you have Eclipse, always use it 3-2 sec before starting a camp to save 3 sec clear time.
• Masteries - I split my points 9/12/9 because she is already that tanky and needs the additional damage and CDR, also MS and increased buff duration are too good to pass up.

Her clear time is actually pretty good if you follow the above rules (solo clear time: 5:00 to red (recall after smite golem for philo stone and clear another camp before red), help at wolves and pull on blue: 5:20 (straight over red golems (wait for some health) and again wraiths and wolves get stone and boots) - but you should gank after lvl 2 anyway so and who cares about your clear time if you got 3 kills by the 5 min mark...), her ganks are astonishing and her sustain in jungle is awesome. Sunfire Aegis and Locket of the Iron Solari should be the Leona items, but they are not that good... :(
I would suggest the following setup, very similar to what you propose in your guide:


and is definitely not bad, but as I said I think a little more HP and a strong Eclipse is all you need. Finally, you might want to turn on comment to vote. I hope this comment helps you :D

not viable. you barely talk about her piss-poor clear times. have fun spending 60 seconds killing wraiths.

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