Turned into one command by Mr.Garretto's Command Combiner, Paxtons_Redstone brings you a new boss! Steps to summon him:
1. Paste and activate the command at the end of this description in a command block.
2. Place a diamond block.
3. Place prismarine bricks over that block.
4. Summon an armor stand on top of that.
5. Wait 30 seconds.
6. ATTACK!
Command: (Works in 1.8+)

/summon FallingSand ~ ~1 ~ {Block:redstone_block,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~ ~ ~1 ~ ~-32 ~1 redstone_block},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~ ~2 ~ ~ ~-33 ~1 air},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~3 ~4 ~ {Block:command_block,Time:1,TileEntityData:{Command:fill ~ ~ ~-1 ~6 ~ ~1 prismarine 1}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add GuardSummon dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add WaterArrow2 dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add WaterArrow dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add Chest dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add WaterGod dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add SummonTime dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add Summon dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add Summon2 dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /scoreboard objectives add Summon1 dummy},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /tellraw @a {text:'by ',color:'white',extra:[{text:'Paxton_Rocks',color:'gold'}]}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command: /tellraw @a {text:'The ',color:'yellow',bold=false,extra:[{text:'Ocean God',color:'aqua',bold=true,extra:{text:' mod has been installed!',color:'yellow',bold=false}]}]}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~4 ~-15 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e[type=Arrow] WaterArrow2 1 {CustomName:"Water Arrow"}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,score_Summon_min=1] ~ ~ ~ summon ArmorStand ~ ~-2 ~ {CustomName:"SummonWaterGod",Invisible:1,NoGravity:1}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand] ~ ~ ~ detect ~ ~-1 ~ prismarine 1 scoreboard players set @e[type=ArmorStand,r=0] Summon1 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~5 ~-14 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[score_WaterArrow2_min=1] ~ ~ ~ particle splash ~ ~ ~ 0 0 0 1 1 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e Summon2 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,name=SummonWaterGod] ~ ~ ~ particle bubble ~ ~1 ~ 0 0 0 1 1 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~6 ~-13 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[score_WaterGod_min=1] ~ ~ ~ effect @a[r=10] mining_fatigue 1 4 false},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e Summon1 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,score_Summon_min=1] ~ ~ ~ fill ~ ~-1 ~ ~ ~-2 ~ air},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~7 ~-12 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e[score_GuardSummon_min=401] GuardSummon 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e[type=Skeleton] WaterGod 1 {CustomName:"Water God"}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players add @e[type=ArmorStand,name=SummonWaterGod] SummonTime 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~8 ~-11 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/effect @a[score_Chest_min=1] water_breathing 1 0 false},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,score_SummonTime_min=200] ~ ~ ~ effect @a[r=5] slowness 1 1 false},Time:1,}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~9 ~-10 ~-1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players add @e[score_WaterGod_min=1] WaterArrow 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,name=SummonWaterGod,score_SummonTime_min=600] ~ ~ ~ summon Skeleton ~ ~ ~ {CustomName:"Water God",Equipment:[{id:diamond_sword,Count:1,tag:{display:{Name:"Prismarine Sword"},AttributeModifiers:{Operation:0,UUIDLeast:1,UUIDMost:1,Amount:10,AttributeName:generic.attackDamage,Name:Blade}]}},{id:diamond_boots,Count:1,tag:{display:{Name:"Prismarine Boots"},ench:[{id:8,lvl:10}]}},{id:diamond_leggings},{id:diamond_chestplate,Count:1,Damage:0,tag:{display:{Name:"Prismarine Chestplate"},AttributeModifiers:[{Operation:0,UUIDLeast:1,UUIDMost:1,Amount:1,AttributeName:generic.knockbackResistance,Name:Sheild}]}},{id:skull,Damage:3,tag:{SkullOwner:"MHF_Squid"}}],Attributes:[{Base:400d,Name:"generic.maxHealth"},{Base:100d,Name:"generic.followRange"}],DropChances:[2:2f,2:2f,2:2f,2:2f,2:2f]}},Time:1,}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~4 ~-10 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[score_WaterArrow_min=400] ~ ~ ~ execute @a[r=8] ~ ~ ~ summon Arrow ~ ~10 ~ {CustomName:"Water Arrow"}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/kill @e[type=ArmorStand,score_Summon_min=1]},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand] ~ ~ ~ detect ~ ~-2 ~ diamond_block 0 scoreboard players set @e[type=ArmorStand,r=0] Summon2 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~5 ~-9 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[score_WaterGod_min=1] ~ ~ ~ particle splash ~ ~ ~ 0 0 0 1 1 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e Summon 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e[type=ArmorStand,score_Summon1_min=1,score_Summon2_min=1] Summon 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~6 ~-8 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players add @e[type=Skeleton,score_WaterGod_min=1] GuardSummon 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @a Chest 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,name=SummonWaterGod] ~ ~ ~ particle splash ~ ~ ~ 0 0 0 1 1 1},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~7 ~-7 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[score_GuardSummon_min=400] ~ ~ ~ summon Guardian ~ ~ ~},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @a Chest 1 {Inventory:[{Slot:102b,id:"minecraft:diamond_chestplate",tag:{display:{Name:"Prismarine Chestplate"}}}]}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/kill @e[type=ArmorStand,score_SummonTime_min=601]},Time:1,}}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~8 ~-6 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,score_SummonTime_min=300] ~ ~ ~ effect @a[r=5] mining_fatigue 1 3 false},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/execute @e[type=ArmorStand,name=SummonWaterGod,score_SummonTime_min=600] ~ ~ ~ tellraw @a {text:"The Water God has been summoned!",color:"blue"}},Time:1,}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:summon FallingSand ~9 ~-5 ~1 {Block:prismarine,Data:1,Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/scoreboard players set @e[score_WaterArrow_min=401] WaterArrow 0},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:/effect @e[score_WaterGod_min=1] water_breathing 1 0 true},Time:1,}}}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:gamerule commandBlockOutput false},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~3 ~-4 ~ ~9 ~-2 ~ redstone_block},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:setblock ~3 ~-3 ~-1 command_block 0 replace {Command:fill ~ ~ ~1 ~6 ~2 ~1 stone 0 replace redstone_block}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:setblock ~3 ~-2 ~1 command_block 0 replace {Command:fill ~ ~ ~-1 ~6 ~2 ~-1 redstone_block 0 replace stone}},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~2 ~-1 ~-2 ~10 ~1 ~2 stained_glass 15 replace prismarine 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~3 ~ ~-1 ~9 ~5 ~1 air 0 replace prismarine 1},Time:1,Riding:{id:FallingSand,Block:command_block,TileEntityData:{Command:fill ~2 ~ ~-2 ~10 ~4 ~2 prismarine 1},Time:1,Riding:{id:FallingSand,Block:stone,Time:1}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}