This is my idea about Bilbo. We all know Bilbo moved to live to Rivendell where he spent his last days "on vacation". As said on Tolkien Gateway:
He lived a very pleasant life of retirement in Rivendell: eating, sleeping, writing poetry, and working on his memoir, There and Back Again and wrote a book called Translations from the Elvish.
So here's a concept which I think fits for the old Bilbo. First of all, he shouldn't be able to fight in close range, since he gave Sting to Frodo, but can still throw rocks. Concerning his abilities, this is what I came up with:
- Master Burglar: Even if old, Bilbo is still an experienced honest burglar. Activating this ability close to an enemy economy building will make Bilbo steal a small amount of resource from it, then quickly make him head to the closest allied base, where he can deliver the bounty. If he's killed during the trip, a tresure chest with the amount of resource stolen will spawn at the place of death. Activating this ability anywhere else on the map will make him stay invisible as long as he stands immobile
This is a mix between the Hobbits' capabilities to conceal themselves and sneak easily with Bilbo's thievery's skills. However, since not having the One Ring, and being old, this ability has two drawbacks: The enemy will be informed of the theft, and the cooldown period of the ability is very long. This should ensure Bilbo is not used too often as a cheap version of Dunlendings or Goblin Pillagers
- Teaching of the Halflings: Hobbits love nothing else than things that grow. For a short period of time, Bilbo teaches the secrets of the land to the selected Hobbit farm, making it produce 30% more resources, but for the duration of the skill he can't move from there nor can he use his skills (except for Master Burglar). If the farm is destroyed before the effect of this skill wears off, Bilbo can be used normally again
- Experienced traveler: In his long life, Bilbo has lived lot of adventures. His memories and experiences influence other heroes. For a short period of time, the selected hero will deal 30% more damage and gain experience faster
- Weaknesses of monsters: Thanks to both his past experience, as well as his studies, Bilbo has learnt anything related to the various monstrosities of Middle-Earth. For a short period of time, the selected allied hero will deal 30% more damage against monsters and gain experience faster
- Need for the One Ring: Even if a brave Hobbit with a pure heart, Bilbo sometimes feels the need to recover the One Ring. If this hasn't been found yet, this ability will temporary show the position of Gollum if he's on a large radius from Bilbo. However, Bilbo's other abilities will be locked for a while. While the effect is activated, Bilbo will move fast, but he loses 50% of his armor but gain double damage, and will attack ANYONE standing on his path to the Ring (since not having a real weapon, he can attack using Gollum's animations)
If the Ring has been already given to a Ringhero, this ability can only be activated if Bilbo is close to it. Activating the ability in this case will make Bilbo viciously attack the Ringhero with triple damage and will also instantly deactivate any effect he has casted on allied buildings/heroes and will scare nearby units and heroes, thus making them lose 15% attack and damage. If he's killed during the effect, he can't be revived for atleast 15 minutes. Otherwise, if he's able to resist and to survive, his abilities will be locked for a while and Bilbo will have 30% less damage and armor since he's scared for what he did
I think this represents Bilbo's personality quite well while he lives on Rivendell: mainly a support figure for Imladris' allies, but with the shadows of the past sometimes resurfacing on the heart of the brave Hobbit. What do you think about it?^^