I think it would be cool if, once the Slayer and Zombie skin line were finished, it would be a 5v5 game mode where one side was the full Slayer champion team and then the other was the full Zombie skin line. Its Howling Abyss and the Slayer skin has a full set of towers while the Zombie skin line has 6 melee and ranged minions per wave, but not towers. The Slayer skin has 1 melee and ranged minion per wave.
Start of the Game:
The game starts and the Slayer team gets till 2:45 to set up and get in position. Then Round 1 begins. At the beginning of Round 1, 7 melee and 7 ranged minions that are Zombie themed spawn for the Zombie team. At 3:30, a random Zombie team player is released from their team's fountain. Then every 45 seconds afterwards, a random one will be released until they are all released. Once Round 2 starts, the Slayer Team will also get 1 siege minion at the start of each round.
The Zombie Team's passive gold generation is increased by 200%, slowly increasing to up to 300% after Round 20. The Slayer Team has 50% reduced passive gold generation, slowly returning to normal until it is back to the normal gold rate after Round 12.
Rounds:
Every 1:15 minutes, the Slayer team will progress a Round. Every Round, each Zombie minion's health is increased by 2.5% more than the health of the last round and attack by 2% of the attack of the last round. Every other round, an additional melee Zombie minion is added to the wave. Every third round, a ranged Zombie minion is added. After Round 12, a super minion will spawn each wave. At Round 16, a second super minion is added. At Round 20, a third super minion is added. At Round 27, all enemy ranged minions are replaced with longer ranged Siege minions with equal range to normal ranged minions. At Round 35, three more super minions are added per wave, equaling six total. Enemy minion waves spawn every 25 seconds for the Zombie team.
During Round 36, the Zombie team gains the Hand of Baron buff.
If the Zombies destroy the enemy Nexus, the spawn time of Slayer champions is increased by 75%.
Slayer Summoner Spells:
Slayer champions have two unique summoner spells: Fortify and Scavenge.
Fortify, after channeling for 2.5 seconds, can be used to make an impassable terrain barricade that only Slayer team units can pass through. The barrier lasts forever, but can be attacked to be destroyed. The barrier has 450 (+50 per level) health. The barrier has 20 (+1 per level) armor and magic resist.
Range: 400
Wall Length: 300 (+15 per level)
Cool Down: 75 seconds
Scavenge can be used to deal 250 (+35 per level) true damage to the target Zombie minion and 50% of that to nearby Zombie minions. The Slayer restores 2.5% max health and 7% max mana for every unit killed by this.
Range: 700
AoE Radius: 250
Cool Down: 50 seconds
Zombie Summoner Spells:
Zombie champions have two unique summoner spells as well: Enrage and Feast.
Enrage causes all nearby Zombie minions to gain 40% movement speed, 65% attack speed, and heal for 3 (+1 per level) health per basic attack for 7.5 seconds. They also take 20% reduced damage from structures during this time.
Range: 775
Cool Down: 180 seconds
Feast can be used within 3 seconds of killing a Slayer unit, causing the user to channel over 5 seconds, restoring 5% max health per second and 15% max mana per second.
Max Range from Killed Unit: 400
Cool Down: 15 seconds
How to End the Game:
The Zombie Team wins by destroying the Slayers' Nexus.
The Slayer Team wins by surviving Round 36.
Spawn Times:
The Slayer team has a spawn rate starting at 25 seconds, increasing to up to 50 seconds after Round 30.
The Zombie team has a spawn rate starting at 12 seconds, increasing to up to 20 seconds after Round 35.