[spoiler=Analysis of Leona, the Radiant Dawn's abilities, in respect to tanking][Q] Leona's Shield of Daybreak:
45/50/55/60/65 Mana
12/11/10/9/8 sec Cooldown
Leona's next autoattack deals an additional 40/70/100/130/160 (+0.3) magic damage and stuns the target for 1.25 seconds.
One of her 3 CC abilities. It pretty much enhances her next autoattack to do more damage + stun the targeted enemy champion. In my opinion, this is best comboed with Zenith Blade to CC the target for at least a total of 2 seconds.
[W] Leona's Eclipse:
60 Mana
14 sec Cooldown
Leona raises her shield to gain 30/40/50/60/70 bonus Armor and Magic Resistance for 3 seconds. When the effect ends she deals 60/110/160/210/260 (+0.4) magic damage to nearby enemies and prolongs the effect for a bonus 3 seconds if any enemies are struck.
I find this skill similar to Rammus's Defensive Ball Curl - in terms of gaining armor and MR while the skill is active - but minus the "Thornmail effect". Once maxed out, this will give her the ability to have lots of damage mitigation, plus able to do a small burst AoE damage to any enemies around her once the 3 seconds effect is up. And the armor/MR gain effect prolong itself for another 3 seconds if she hits any enemies with her small AoE burst. I'd say this skill is a must have to use in any teamfight.
[E] Leona's Zenith Blade:
60/65/70/75/80 Mana
13/12/11/10/9 sec Cooldown
700 range
Leona projects a solar image of her sword which deals 60/100/140/180/220 (+0.4) magic damage to all enemies in a line. When the image fades the last enemy champion struck will be briefly immobilized and Leona will dash to them.
Until I get a closer look at her, I'll go out on a limb and say this is her initiation skill. If this ability is used on a single champion, it will pretty much stop him or her in place. And since it hits the last champion in line, I think this is a very good skill to target squishies. Since they are usually in the back, Leona can pretty much bypass the tanks - hopefully, if the skillshot is aimed correctly - and can go after the squishies, triggering a teamfight.
This ability is best used along with Shield of Daybreak [Q] ability because it will allow her to CC the targeted enemy champion for at least 2 seconds.
[R] Leona's Solar Flare:
100/150/200 Mana
105/90/75 sec Cooldown
1200 range
After a brief delay Leona calls down a beam of solar energy to deal 150/250/350 (+0.8) magic damage and slow enemies by 80% for 1.5 seconds. Enemies in the center of the effect are stunned instead of slowed.
Her signature skill, the giant AoE burst that Riot has been talking about for some time. Best used when the enemy is clustered together. Anyone that is in the center of the AoE burst will pretty much be stopped in their tracks. Either way, anyone who gets hit with this skill will be heavily CC'd as well as suffer a bit of damage.
If you can find a bunch of enemies clustered together and you drop this on them, you're pretty much good to go. And if you're able to stun any squishy carry champs, that's a plus.
Though IMO, that 80% slow is a bit too much. I think it could be toned down later on.[/spoiler]