Minecraft – Using command blocks to spawn player-killed mobs

Some servers restrict iron drops from iron golems to prevent the building of giant automated farms, or restrict any drops from environmentally-killed monsters, again, to prevent the creation of giant automated farms.

This might be done for gameplay reasons (no supplies of infinite free stuff) or for server lag reasons (no concentrations of hundreds or thousands of monsters collected in a tiny spot).

A player can spawn on any solid block which is not affected by gravity and is below the sky, so there are no blocks above it.

Animals spawn on grass or dirt exclusively (block id 2 and 3). They also require a light level above 9 and at least 2 blocks of air above them. Exception is the bat, which spawns on opaque blocks if the light level is below 9.

Skeletons, Zombies, and Creepers can spawn on any opaque block if the light level is below 7. Exception are mobs in the nether, which can spawn on netherrack, no matter what the light level is.

Opaque blocks include:

1      --> Stone
1:1    --> Granite
1:2    --> Polished Granite
1:3    --> Diorite
1:4    --> Polished Diorite
1:5    --> Andesite
1:6    --> Polished Andesite
2      --> Grass
3      --> Dirt
3:1    --> Coarse Dirt
3:2    --> Podzol
4      --> Cobblestone
5      --> Oak Wood Plank
5:1    --> Spruce Wood Plank
5:2    --> Birch Wood Plank
5:3    --> Jungle Wood Plank
5:4    --> Acacia Wood Plank
5:5    --> Dark Oak Wood Plank
12     --> Sand
12:1   --> Red Sand
13     --> Gravel
14     --> Gold Ore
15     --> Iron Ore
16     --> Coal Ore
17     --> Oak Wood
17:1   --> Spruce Wood
17:2   --> Birch Wood
17:3   --> Jungle Wood
35     --> White Wool
35:1   --> Orange Wool
35:2   --> Magenta Wool
35:3   --> Light Blue Wool
35:4   --> Yellow Wool
35:5   --> Lime Wool
35:6   --> Pink Wool
35:7   --> Gray Wool
35:8   --> Light Gray Wool
35:9   --> Cyan Wool
35:10  --> Purple Wool
35:11  --> Blue Wool
35:12  --> Brown Wool
35:13  --> Green Wool
35:14  --> Red Wool
35:15  --> Black Wool
41     --> Gold Block
42     --> Iron Block
43     --> Double Stone Slab
43:1   --> Double Sandstone Slab
43:2   --> Double Wooden Slab
43:3   --> Double Cobblestone Slab
43:4   --> Double Brick Slab
43:5   --> Double Stone Brick Slab
43:6   --> Double Nether Brick Slab
43:7   --> Double Quartz Slab
45     --> Bricks
47     --> Bookshelf
48     --> Moss Stone
49     --> Obsidian
56     --> Diamond Ore
57     --> Diamond Block
78     --> Snow
80     --> Snow Block
87     --> Netherrack
97     --> Stone Monster Egg
97:1   --> Cobblestone Monster Egg
97:2   --> Stone Brick Monster Egg
97:3   --> Mossy Stone Brick Monster Egg
97:4   --> Cracked Stone Brick Monster Egg
97:5   --> Chiseled Stone Brick Monster Egg
98     --> Stone Bricks
98:1   --> Mossy Stone Bricks
98:2   --> Cracked Stone Bricks
98:3   --> Chiseled Stone Bricks
99     --> Brown Mushroom Block
100    --> Red Mushroom Block
159    --> White Stained Clay
159:1  --> Orange Stained Clay
159:2  --> Magenta Stained Clay
159:3  --> Light Blue Stained Clay
159:4  --> Yellow Stained Clay
159:5  --> Lime Stained Clay
159:6  --> Pink Stained Clay
159:7  --> Gray Stained Clay
159:8  --> Light Gray Stained Clay
159:9  --> Cyan Stained Clay
159:10 --> Purple Stained Clay
159:11 --> Blue Stained Clay
159:12 --> Brown Stained Clay
159:13 --> Green Stained Clay
159:14 --> Red Stained Clay
159:15 --> Black Stained Clay
179    --> Red Sandstone
179:1  --> Smooth Red Sandstone
179:2  --> Chiseled Red Sandstone

I hope I didn't forget any, if I did, feel free to add them.