Kill

A kill is the event of decreasing an enemy champion's health to zero while the enemy has no abilities or Items to prevent death. Death may be prevented by certain effects, such as those granted by the item Guardian Angel and friendly abilities like Zilean's Chronoshift, or delayed by passive abilities like Anivia's Rebirth, Zac's Cell Division and Aatrox's World Ender.

Rewards

The last player to strike the target champion is awarded with the kill, and all contributors within the last 10 seconds are awarded with an assist. If the champion killed has any transferable buffs ( Crest of Insight or Crest of Cinders), the killer champion gains all of these buffs and the duration of each buff is reset. When a champion is killed, the player who scored the final hit receives gold and experience. Additionally, a champion with many consecutive deaths will award a significantly reduced bounty, while one with many consecutive kills will award a higher bounty (refer to Bounty values Notes below for details).

Experience Reward

Experience received is equal to (90 + 50 × level of the champion slain). If another champion assists in the kill, the experience is split in half, equaling (45 + 25 × level of the champion slain). If three champions participate in the kill, the experience is split in thirds, equaling (23 + 17 × level of the champion slain).

This is increased or decreased by 7% per level difference between the killer and the slain champion, but cannot be lower than 20%.

Execution

If a champion dies and hasn't been damaged or debuffed by another champion in the last 13 seconds, they are executed. Otherwise, the kill is awarded to the enemy champion who last dealt damage. Executions are caused by a turret, minion, or monster. An execution offers no gold but still grants experience to nearby champions on the opposite team when it is caused by a turret or minion.

In some cases it could be strategically advantageous for a player to purposefully be executed as an alternative to dying from an enemy champion; in doing so, the enemy receives no gold. Doing this on ARAM allows you to visit the shop without granting kills to the enemy team.

Note that executions do not count as deaths for the purposes of resetting bounties, death streaks or kill streaks.

Multi-kill

The act of killing several champions within 10 seconds of each other (30 seconds to Penta Kill after a Quadra Kill if no enemy respawns). The following comments are shown: "Summoner" has slain "(slain name) Summoner" for a [...]!'

Double Kill (2)
Triple Kill (3)
Quadra Kill (4)
Penta Kill (5)
Hexa Kill (6)

History

Some footage from before the time where Hexakill was introduced shows the possibility of getting a Legendary Kill, which can occur after killing another enemy after a Penta Kill, on any gamemode other than Hexakill.

However this feature seems to have been removed from the game, and the time at which it occurred is uncertain.

Legendary Kill

Legendary kill is still in the game but it will only work when you get a penta kill & than kill 3 more when they respawn. You can only have 8 seconds between your penta & your next kill. In order to achieve this you need to be able to get into their base before 15 minutes. This can only be achieved with two or more players.

Source: https://www.youtube.com/watch?v=uEkiKHldSvo

Ace

An ace is defined as killing the last living champion of the enemy team. Scoring an ace is far easier than scoring a pentakill, since the only requisite is for the entire allied team to kill the enemy team, rather than one person killing the entire enemy team. There is no gold bonus associated with aces.

Bounties

Teams earn gold rewards when they kill enemy champions. This reward is the bounty of the killed champion. The bounty of a champion depends on his number of consecutive kills or deaths. The number of consecutive kills a champion has is the number of times he has killed enemy champions since he last died or since the match began. The number of consecutive deaths a champion has is the number of times he has died since he last killed an enemy champion or since the match began. The more consecutive kills a champion has, the bigger his bounty. The more consecutive deaths a champion has, the smaller his bounty.

Bounties are divided into two parts:

Kill bounty: Earned by the champion who deals the killing blow.
Assist bounty: Shared evenly among the champions who assist in the kill.

Each part of the bounty is calculated using a system of tiers numbered from -9 to 8. Kill bounties in higher tiers are bigger. Each champion starts the match in the bounty tier 0 and moves to other tiers as he kills enemies or dies. Consecutive kills move a champion to a higher tier, while consecutive deaths move him to a lower tier.

This table shows the number of consecutive kills or deaths required to access each tier, and the bounty earned by killing a champion in that tier:

Tier	Consecutive kills	Consecutive deaths	Kill bounty	Assist bounty	In game announcement
8	8+		1000 (+ 100 per kill beyond the 7th).	150	Legendary
7	7		1000	150	Godlike
6	6		900	150	Dominating
5	5		800	150	Unstoppable
4	4		700	150	Rampage
3	3		600	150	Killing spree
2	2		450	150
1	1		300	150
0	0	0	300	150
-1		1	274	137
-2		2	220	110
-3		3	176	88
-4		4	140	70
-5		5	112	56
-6		6+	100	50

CS gold = amount of gold earned from minions, monsters and support items.
Tier resets to 0 when dying while being on a positive tier or when doing a kill on a negative tier.
Champions with negative tiers also have their tier increased by 1 for each 1000 gold earned from CS or by earning an assist.
First blood gives 100 bonus gold to the kill bounty and 50 to the assist bounty.
If, since their last death, a champion has earned 300 more gold from CS than the enemy team's average during that time, their bounty increases by 50 gold, plus another 50 gold for each additional 200 gold their advantage grows by thereafter. The amount is dynamic and is reduced if the player loses the advantage.
- Average is determined by dividing the enemy team's CS gold by 4.3, rather than five, based on the four sources of income on Summoner's Rift (top/mid/bot/jungle) + support item income. Modes with smaller teams divide by the number of champs per team instead (ex. 3 for Twisted Treeline).
If you die with less CS gold than the enemy team's average, you'll respawn with a buffer equal to the difference. You won't start accruing a CS gold bounty until you've used up the buffer.
All bounties, excluding base bounty, of a team are reduced by 20% if their total team gold is 3% lower than the opposing team's gold. The reduction is increased to Error: Parameter '3' is not accepted. and further increased to Error: Parameter '3' is not accepted..
Total assist bounty is reduced to Error: Parameter '3' is not accepted..
Bounties do not increase mid-combat. If a champion earns multiple kills and then immediately dies, those kills will count toward their next death instead.
A single kill cannot grant more than 1000 total gold to the killer.
- Since a champion's bounty can stack to greater values, any remaining gold will carry over. Because of this, enemies can be 'Shutdown' multiple times in succession.
Bounties over 150 gold (before bounty reduction from team gold deficit) are visible in the scoreboard to both allies and enemies.

Triggering effects with kills

Champion abilities, items and runes that trigger an effect with a kill or assist can be seen on the takedown page.

Champion abilities

Champion kill

The following abilities will trigger an effect upon killing an enemy champion, they will not trigger with an assist:

Any unit kill

The following abilities will trigger an effect upon killing any unit:

Items

The following items will trigger an effect upon killing any unit:

Phage and its upgrades ( )

Runes

References

League of Legends Wiki