League of Legends (LoL) Question: A question about jungling

There are only two ways to bring jungle monsters to fight with you. The first is the Rift Herald who drops an item when slain that can be picked up by the killer's team and used to summon the Herald to push down the nearest lane. The Herald does a lot of damage to towers, but won't attack champions directly.

The other way is to have a Mordekaiser on your team. Upon killing or assisting in a kill on the Dragon, Mordekaiser gains control of a ghostly copy of the Dragon that he can control. Mordekaiser must have Children of the Grave (his ultimate ability) skilled up in order to get a ghost dragon.

If you're seeing other non-champion units, those are pets, which are summoned units unique to different champions. For example, Annie can summon a giant bear with her ultimate: Summon: Tibbers.