Don't think that the kit really matches the image you provided well. A piper character like him would either be doing his piping to mess with enemies or be controlling the damage dealing monster in some way remotely, such as making him a true permanent pet-controlling champion. The pet could behave in response to his abilities, instead of just being the character, really (the piper is redundant in the kit). As it is, all of the abilities are based around just the mini Baron beast, and overall the image just makes me think of this: https://78.media.tumblr.com/a44d924c6e4ed0b64e993a727dc686f2/tumblr_n4jjbu3dO31qzcxzqo4_400.gif instead of a character I'd be excited to play.
Here, try this:
Your pet is a separate entity that can be alt-clicked to move around but otherwise has it's own rudimentary ai (like a better Daisy from Ivern or Tibbers from Annie, since it's a permanent pet). It can't die, but it can be hurt to the point where it has to retreat, in a way not unlike Skaarl runs away from Kled when they take too much damage.
Passive: Loyalty -> Your pet immediately prioritizes its attacks on opponents that get within 300 units of you, gaining a scaling enrage that buffs its attack speed if you are attacked. Additionally, if your pet drops below a certain health level (with its stats being tied to a percent of your stats), it quickly retreats to you, providing you with an overshield (that has to be eaten through before getting to you) for a period of time until it is able to return (based on level, scaling).
Q: Pipe Dream -> You play a dope beat (wide skillshot!) that, upon hitting allies (or your pet), will increase their movement speed. Hitting enemies with this will slow them briefly and allow your pet to put a stacking de-buff that (similar to Braum's passive) will put an afflicted enemy to sleep briefly.
W: [Sludge Bomb was too much like a better version of Ziggs' w as is] Scooby Mini-Baron Snack -> You throw a disgusting (or, depending on your perspective, delicious) pile of rotten meat on the ground. Enemies that step on it destroy the snack get briefly feared. If your pet runs over it, it gains some health back and an attack damage steroid.
E: Tactical slide [charges up like Vel'Koz's W] -> You slide in a given vector direction. If you bump into your pet, you can pick him up and toss 'im. Deals true damage to enemies hit (based on level, %AD).
R: Growth Hormone -> You dash excitedly at your pet and inject them with a solution that causes them to hulk into a Behemoth on which you ride into battle (lasts up to a given number of seconds and such), controlling their abilities:
Passive: Ichor Armor -> Attacks on your creature cause pustules to burst poison that trails behind it as it moves; Your health is also partially tied to your monster (if it falls, you're going to be very low on health while running away, and there's no overshield protecting you).
Q: Ravage -> Sweeps its Claws/Mandibles in front of it, throwing enemies back to the extremes of it autoattack range.
W: Chomp -> take a bite out a nearby minion or champion, gaininig a percent of the damage back as health.
E: Tactless charge -> You charge a large distance forward, pushing enemies with you and damaging them more the further you travel with them.
R: Last Stand -> Your pet roots itself in the ground and flings you off behind it, with you personally getting a minor movement speed buff. It begins wildly auto-attacking anything in front of it like a turret. At the end of a given amount of time based on rank or level, your pet 'expires' and has to retreat to you [no overshield, but you'll have cover fire to escape].
And that's it. Don't know if you like any of it or whatnot. The piper aspect is still shady at best. Best!
