Hextech Tracking Mite
The Hextech Tracking Mite would be a champion ability that sticks a tracking unit onto an enemy champion or large/epic monster. This unit grants vision of the target until it is destroyed via the afflicted's ally's autoattacks or any autoattacks on neutral camps (it has a small health bar). When killed, the Mite will self-destruct, dealing damage to the target and possibly applying grievous wounds (since it's burrowed under the skin and caused internal damage).
In the early game, this spell is used to tag opposing laners or the enemy jungler to lessen roam potential and "ward" enemy camps to get a rough estimate of timers for them. By tagging a jungler or solo laner, this spell encourages frequent visits to lanes by junglers purely to deal with the bug, similar to how junglers enter brushes after using a scrying plant only to kill the ward and then leave. In bot lane, the Mite can be dropped on the enemy support to keep them from roaming mid or deep warding your jungle without your knowledge, and if the ADC tries to get it off of them, they leave themselves open to being traded with unfavorably.
Towards mid and late game, the spell falls off, now that teams group and stragglers are replaced by dedicated splitpushers, however it is still useful in getting vision control on Dragon and Baron/Herald. Additionally, placing one on the Rift Scuttler can provide a mobile ward in the river. To counter this lack of ultility in getting vision on enemy champions, the detonation's scaling is insane with each point put in, balanced out by it being an ability that is meant to be amxed last in the scheme of the kit. In fights, if you expect a target to soon disengage, place one on them to either drag an ally back with them to dispose of it so they can safely back, or pinpoint their location of recall for an ally with a global ult (or just really long spell like a Jhin W) to finish them off and/or interrupt their back if you have an ally splitting their base during said fight. Aside from all that, the spell still functions well as a baby Tristana E.
This ability's minion will be protected by Bard R's stasis, but not by a Zhonya's or Stopwatch's stasis, making these items handy for safely removing them. The counter to this item is having an ally with shields or one that can self-cast (but then those help against everything). This spell synergizes with long-range champions, both in ability distance (global ults), champions that can clear the map quickly (Hecarim, Quinn, Rammus), and is an excellent tool to boost viability in buying Righteous Glory. The spell's health bar has potential as a disengage as it can disrupt an enemy's attack move to aid in your escape when being chased. Only two Mites can be planted at any time, and one of the two active must be destroyed before another can be placed. If an enemy champion dies with this spell attached to them, it detaches, falling onto the ground on their corpse, and initiates a self-destruct sequence over the course of a second, inflicting half the damage it would normally cause in a tiny AOE.