An Aggressive Jungle Creep!
I think it would be really cool if there was a more "aggressive" creep on Summoner's Rift or Twisted Treeline. It would be "aggressive" in the sense that it would attack unprovoked, hence working as an obstacle to map movement that the jungler would be responsible for. In other words, it would make a new type objective (make the map safer for my team) accessible to both junglers. I'm thinking it would spawn later than the normal jungle monsters, maybe even at the same time as dragon. I think that any creep with this trait would have to have well-defined standards for when/who it wants to attack at any point (maybe always aiming for the lowest health champ for instance, or always sticking to the same target), otherwise they would be too much of a random element. Besides those broader ideas, I have a few, probably bad, ideas for what the creep could be like, but regardless if any of them are viable I think the idea of an aggressive monster in the jungle would be super cool. My first idea is something like a mini rengar-type creep. It would be constantly stealthed (until it is engages in combat of course), and it would roam in a cyclical pattern around blue (maybe red? don't know which would be better). It would have low health, but significant damage reduction either as a percent based passive (takes 50% less magic/physical damage) or lots of armor and mr. The point of this would be to make it hard to kill without true damage (either smite or jungle item based), thus making it a real threat for non-jungle champions in the mid game and giving the jungler more responsibility and importance for the objective. It would definitely have melee autoattacks, but it might also have a slow (or an execute? maybe too strong lol). I think it would be cool if it only attacked/seeked low-health champs (something like 50% maybe?) or had a bonus for attacking from stealth, as it would really emphasize the importance of vision in your own jungle. Another thought I had was that the creep could be a controllable one sided threat, maybe even a "sentinel" or "guard" type monster. I was thinking like a monster on one side of the map (like baron or dragon) that pops up around the same time as blue/red. the creep would at first be passive like other creeps, but if one team kills it, it will re-spawn for some time as an "allied" creep, either appearing where it already was or in some important part of either teams' jungle. Once re-spawned it will behave "aggressively" towards the enemy team, attacking on sight. I can imagine it with ranged autoattacks if it is a stationary creep, but melee if it can move. I like to think of it as possibly even behaving like the redeads in legend of zelda with a single aoe stun that it might use at the beginning of it's attack pattern, making it's area a dangerous place for the enemy team to fight. Alternatively, the creep could behave as a type of "buff" by actually following around the player that killed it and blindly attacking enemy champions within a certain range of the allied champion (but not attacking creeps, cuz that would be op). The last even remotely cool idea I could come up with was inspired by the baron tail attack that pops out of the ground. Essentially, it would be an "underground" creep. It would exist as an untargetable object (like vlad or fizz) some of the time. Unlike normal jungle creeps, it would have either little or no health regen, keeping whatever damage it takes. I envision it using guerrilla tactics. It would either start underground before bursting up for a surprise attack, staying above ground for a short time as it attempts to run away. Or, it could start above ground before diving for a short to medium period of time, dealing damage while untargetable like vlad, and then having a moment of vulnerability after this state is exhausted. Both ways its weakness would be burst damage and cc. One or both are provided by most/every jungler (smite provides burst to everyone at least). I'm not sure when this guy would pop up, but I figure it would at least be after the point where the jungler should have gotten his first buff.
TLDR for people who don't like text walls: It would be cool if there as a creep, either stationary or wandering around the jungle, who took the initiative to attack champions on its own, either on both sides or team specific.