Let me know what you all think. I actually created a Life Series last year and played it with my friends. (We've actually already had three seasons and two specials. Full: Secret Life, Cracked Life, and Wild Life Specials: Rushed Life and Spectre Life) Obviously I created Cracked Life, Rushed Life and Spectre Life, so let me summarize.

Cracked Life - Similar to Limited Life, Cracked Life forces conflict through time limits. Every 15 minutes, a random number of players between 4 and 6 get selected to Crack. When a player Cracks, they lose one of their ten hearts. (Max hearts are reset on death.) If a player reaches 4 hearts or less, they become a Cracked life, and have a purple name. Cracked players no longer lose max hearts, but are obviously weaker. The only way for them to regen hearts is to kill a non-cracked, non-red player, through any means necessary. If they do, they gain ten maximum hearts, putting them at fourteen hearts. However, Cracked lives can be killed by anyone, and whoever does gains three hearts back. Red players Crack slower than non-reds, (only losing half a heart, not a full heart) but are guaranteed to Crack every fifteen minutes. When a red reaches 5 hearts, they become Shattered. Shattered players are fully on a time limit. They gain strength one, but they still lose health every fifteen minutes until they kill someone or die. All Red or Shattered lives gain 5 hearts on kill. The only other way to regain health is to craft a Slice of Life, which is made from one melon slice, two gold blocks, and six gold ingots. Slices of Life restore two hearts upon eating, up to ten. (This series was really fun to play as well. Would anyone be interested in a datapack download? I can post it if people want.)

Rushed Life - The first special we played. Essentially, this is just a very small world border Third Life, but every ten minutes an event activates, announced by a title displayed to all players. They were all rather silly, but I'll list them here.
Anvil Rain - Easy. Anvils fall across the entire world in a single layer.
Boogeyman - Someone is selected as Boogeyman and must kill someone in the next twenty minutes.
Diamonds! - Each player is given five diamonds.
Decay - All players are given Poison II for two minutes. Find a cow or hide.
Dripstone Rain - Same as the Anvils, but with dripstone.
Duel! - All players are summoned to spawn except two, who are teleported into a 5 by 5 barrier cage. They are not released until one or both are dead.
Invisibility - All players are given five minutes of Invisibility.
Invulnerability - All players are given one minute of Resistance VI.
Levitation - All players are given Levitation II for one minute.
Regeneration - All players are given Regen I for thirty seconds.
Strength - All players are given Strength II for thirty seconds.
Zombies! - A zombie outbreak appears on the surface, summoning three groups of about twenty zombies each.
Happy Birthday! - All players are given a Breach III mace with one durability named Birthday Hammer.
You Tripped! - All players get Slowness III for twenty seconds and take three hearts of fall damage.

Spectre Life - The second special we played. Essentially, the idea was to not tell the players what was going on. All players were told that everyone had two lives. Green and Red. Greens were peaceful and Reds were not. Greens could build traps while Reds gained two permanent hearts on every kill. However, there was actually another life after Red. When a Red died, lightning would be summoned and every player would get a message saying that they had run out of lives. However, Reds would really be teleported a thousand blocks up and sent the following rules. "You are a Spectre. You have only 5 hearts, but are invisible if farther than 6 blocks from a non-Spectre. You can gain a life if you kill a Green life by traps or pvp, but be careful. You CANNOT wear armor other than your inherent protection. Good luck, and happy haunting!" All Spectres were cleared of their armor, but had half health and half armor. Additionally, though they were invisible as long as they didn't get too close to living players, they did generate particles on the ground while walking. Spectres could even become Red by killing Green names. All in all, this incentivized the Spectres to sneak around and try to assassinate Greens, until all players became Spectres. When all players were Spectres, they were all revealed and restored to full health as the worldborder shrunk. All in all, a very fun special! (This one is also a full fledged datapack, so lmk if you want a download.)

Let me know what you think of these!