With the move to the loot tables in 1.9, some of the mob drops are no longer happening with a FakePlayer - or I've not coded it correctly.

There does seem to be a "condition": "killed_by_player" which may be part of the issue.

It is set for:

blaze - blaze rods
spider - spider eye
zombie - iron_ingot, carrot, potato
etc

So this needs some investigation.

So with some quick debugging:

The getKillerPlayer method of LootContext is returning null for a FakePlayer.
EntityLivingBase.onDeath
this.getAttackingEntity() = null

In 1.8.9:

OnDeath just called dropFewItems, which in the case of EntityBlaze just added blaze_rod if rng said yes.

In 1.9.0 we are now using the loot tables:

OnDeath now calls EntityLiving.dropLoot which uses the loot tables.
onDeath->dropLoot->generateLootForPools->generateLoot->testAllConditions.
It is testAllConditions that processes the "killed_by_player", however the player is null for the FakePlayer.

KilledByPlayer->testCondition. context.getKillerPlayer = null

So I might have to put a workaround in for vanilla, to fake generate these extra items, until I can work out how the loot tables are supposed to be processed with the FakePlayer.

So the answer is that I'm not hitting the entity first before killing it. If I attack the entity with the fake player then the attackingPlayer would be set and the loot would be dropped. So I can either call atttackEntityFrom with an amount of 0 or just directly set the attackingPlayer value.

The attackingPlayer field is protected, so with a little access transformer magic I can set that value to the fakePlayer and the blaze now drops blaze rods. Need to see if there is a better way of doing this before going with the access transformer method.