Nexus Obelisk

The Nexus Obelisk is a special type of turret. It is located at each team's spawning pool and has no health, as it cannot be targeted or damaged. On Summoner's Rift and Twisted Treeline, the Nexus Obelisk is near the Shop on each team. The Nexus Obelisk isn't present on Proving Grounds. On Crystal Scar, there are 3 Nexus Obelisks on each team: 2 located on the base entrance, and one near the shop. It deals 1000 true damage per shot with an attack speed of 2.0. Its damage is not blocked by any type of defensive abilities or stats such as armor, magic resistance. Like other towers, it does detect stealth.

Abilities and items ignored
Champions that have any of these and walk into range of the Obelisk will be unaffected by any of those effects and will be killed immediately.

A champion that is revived by Omen of Death will have another death if they are targetted by the Obelisk too.

Abilities and items unaffected
Using these abilities and/or item at the right time within the Obelisk's range will prevent damage for that given time.

Strategy
The obelisk can be used as a weapon when defending the Nexus if the enemies are close or near the range of the Obelisk. Champions with fear, knockback, pull, suppression, and taunt abilities can force enemies into the range of the Obelisk and quickly burn down their health or even killing them. Baiting the attacker (melee) into the Obelisk's range can also bring the same result.