When fighting the dragon, the game crashed. This happened after all the crystals were destroyed.
1 crash was when the dragon was around 3/4th the health.
2nd crash was when the dragon had less than 1/2th health.
When trying to load up the world after the second crash, it would always crash immediately.

---- Minecraft Crash Report ----
// Don't be sad, have a hug! <3

Time: 8/5/15 10:53 AM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at vn.k(SourceFile:69)
at vn.j(SourceFile:65)
at vn.c(SourceFile:30)
at va.m(SourceFile:227)
at qj.t_(SourceFile:1404)
at qk.t_(SourceFile:228)
at afk.a(SourceFile:1407)
at lg.a(SourceFile:599)
at afk.g(SourceFile:1385)
at afk.j(SourceFile:1278)
at lg.j(SourceFile:480)
at net.minecraft.server.MinecraftServer.B(SourceFile:607)
at net.minecraft.server.MinecraftServer.A(SourceFile:535)
at btd.A(SourceFile:152)
at net.minecraft.server.MinecraftServer.run(SourceFile:451)
at java.lang.Thread.run(Thread.java:745)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at vn.k(SourceFile:69)
at vn.j(SourceFile:65)
at vn.c(SourceFile:30)
at va.m(SourceFile:227)
at qj.t_(SourceFile:1404)
at qk.t_(SourceFile:228)
at afk.a(SourceFile:1407)
at lg.a(SourceFile:599)
at afk.g(SourceFile:1385)

– Entity being ticked –
Details:
Entity Type: EnderDragon (va)
Entity ID: 271
Entity Name: Ender Dragon
Entity's Exact location: 0.07, 62.54, 0.68
Entity's Block location: 0.00,62.00,0.00 - World: (0,62,0), Chunk: (at 0,3,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Entity's Momentum: -0.53, 0.40, 0.49
Entity's Rider: ~_ERROR~ NullPointerException: null
Entity's Vehicle: ~_ERROR~ NullPointerException: null
Stacktrace:
at afk.j(SourceFile:1278)
at lg.j(SourceFile:480)

– Affected level –
Details:
Level name: Dragon Fight
All players: 1 total; [lh['MightyBurger'/222, l='Dragon Fight', x=5.06, y=61.36, z=-5.02]]
Chunk stats: ServerChunkCache: 289 Drop: 0
Level seed: 449128878844457348
Level generator: ID 00 - default, ver 1. Features enabled: false
Level generator options:
Level spawn location: 0.00,0.00,0.00 - World: (0,0,0), Chunk: (at 0,0,0 in 0,0; contains blocks 0,0,0 to 15,255,15), Region: (0,0; contains chunks 0,0 to 31,31, blocks 0,0,0 to 511,255,511)
Level time: 0 game time, 0 day time
Level dimension: 0
Level storage version: 0x00000 - Unknown?
Level weather: Rain time: 0 (now: false), thunder time: 0 (now: false)
Level game mode: ~_ERROR~ NullPointerException: null
Stacktrace:
at net.minecraft.server.MinecraftServer.B(SourceFile:607)
at net.minecraft.server.MinecraftServer.A(SourceFile:535)
at btd.A(SourceFile:152)
at net.minecraft.server.MinecraftServer.run(SourceFile:451)
at java.lang.Thread.run(Thread.java:745)

– System Details –
Details:
Minecraft Version: 15w32a
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_25, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 87337888 bytes (83 MB) / 299368448 bytes (285 MB) up to 3132096512 bytes (2987 MB)
JVM Flags: 3 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx3G -Xmn256M
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 94
Profiler Position: N/A (disabled)
Player Count: 1 / 8; [lh['MightyBurger'/222, l='Dragon Fight', x=5.06, y=61.36, z=-5.02]]
Type: Integrated Server (map_client.txt)
Is Modded: Probably not. Jar signature remains and both client + server brands are untouched.