(Champion Concept) Piggy - The Piggybacker

Right, So I have been coming up with ideas for champions in my head and this one seems like it would work (kind of) (Apologies for not having anything visual, it's just sort of an idea)

Let's start with the ult, the most vital part of the champion; R - Mount - 30 Mana - 20 second cooldown (can be cast again ignoring cooldown if already mounted) - Available from Level 1 "Piggy mounts the selected character and depending on what you mount it will have different effects;

1. Level 1 - Mount minions/Champions - Allows you to control minions giving them a slight boost in AD/MD (Depending on the minion you mount)/ Allows you to mount an enemy/allied champion (if mounting a enemy, slows their movement speed for 20/30/40/50/55%. If mounting an ally, increases their movement speed for 30/40/50/60/65%. Any damage done to the ally is split between them and Piggy)
2. Level 2 - Mount Jungle minions - Allows you to mount any jungle creep except for the buffs, again providing them with a small buff to their AD.
3. Level 3 - Mount Jungle buffs - Allows you to mount any buff within the jungle, any attacks used with the minion apply the buff's effect.
4. Level 4 - Mount Dragon - Allows you to mount the dragon, provides the dragon with 25% less damage taken from attacks and allows you to use the dragons abilities against your foes." (My original thought was "Mount Baron Nashor" but that would go a bit too far) If a minion/dragon dies while you are mounting them, you lose a portion of your health depending on the minion/dragon you are mounting (~15% for minion, 40% for dragon)

Since Piggy's Mount is vital to his play-style, his other abilities help him while he is mounting something.

Q - Piggyback Acceleration - 50 Mana, *7/6.5/6/5.5/5 *second cooldown "Speeds up the current mount by 20/30/40/50% for 3 seconds" This is for catching up to enemies in order to finish them off or to initiate but can be used as an escape method.

W - Piggyback Attack - 40 Mana,* 6/5.5/5/4.5/4* second cooldown "Attacks a nearby targeted enemy for 30/35/40/45/50% of your current mount's ability power/attack damage + your ability power (whichever is higher)" This would be as your primary way of damaging enemies.

E - Piggyback Heal - 70 Mana, 15,14,13,12,11 second cooldown "Heals current mount for 20/25/30/35/40% of their health over 10 seconds" This would benefit your team in 5v5s as you can heal a vital ally in order to stall/prevent a death from a global ult.

Post any suggestions on nerfs/buffs that should happen.