Using the follow spell will cause a ticking tile entity error and the server will crash and continue to crash until you delete the tile entity:

Bullet Type: Projectile
Spell:
{spellName:"Wither Shot",uuidMost:2265479176460060427L,validSpell:1b,spellList:[0:{spellPosX:2,spellData:{spellKey:"selectorFocalPoint",params:{}},spellPosY:3},1:{spellPosX:3,spellData:{spellKey:"operatorFocusedEntity",params:{psi.spellparam.target:3}},spellPosY:3},2:{spellPosX:4,spellData:{spellKey:"constantNumber",params:{},constantValue:"1"},spellPosY:2},3:{spellPosX:4,spellData:{spellKey:"trickWither",params:{psi.spellparam.time:2,psi.spellparam.power:1,psi.spellparam.target:3}},spellPosY:3},4:{spellPosX:4,spellData:{spellKey:"constantNumber",params:{},constantValue:"2"},spellPosY:4}],uuidLeast:-7159187827430677625L}

Crash log:
---- Minecraft Crash Report ----

WARNING: coremods are present:
NowWithRendering (hopperducts-mc1.8.8-1.4.6.jar)
LoadingPlugin (RandomThings-MC1.8.9-3.6.2.jar)
thaumicinfusion (ThaumicInfusion-1.8.9-4.82.jar)
ThaumcraftLoader (Thaumcraft-1.8.9-5.1.6.jar)
FldLoadingPlugin (FastLeafDecay-1.8-1.6.jar)
dsurroundcore (DynamicSurroundings-1.8.9-2.0.4.10.jar)
Contact their authors BEFORE contacting forge

// Shall we play a game?

Time: 2/22/16 7:48 PM
Description: Ticking entity

java.lang.NullPointerException: Ticking entity
at vazkii.psi.api.internal.Vector3.(Vector3.java:62)
at vazkii.psi.common.spell.operator.vector.PieceOperatorVectorRaycast.raycast(PieceOperatorVectorRaycast.java:70)
at vazkii.psi.common.spell.operator.entity.PieceOperatorFocusedEntity.getEntityLookedAt(PieceOperatorFocusedEntity.java:60)
at vazkii.psi.common.spell.operator.entity.PieceOperatorFocusedEntity.execute(PieceOperatorFocusedEntity.java:48)
at vazkii.psi.api.spell.CompiledSpell$Action.execute(CompiledSpell.java:95)
at vazkii.psi.api.spell.CompiledSpell.execute(CompiledSpell.java:51)
at vazkii.psi.api.spell.CompiledSpell.safeExecute(CompiledSpell.java:70)
at vazkii.psi.common.entity.EntitySpellProjectile.cast(EntitySpellProjectile.java:211)
at vazkii.psi.common.entity.EntitySpellProjectile.cast(EntitySpellProjectile.java:187)
at vazkii.psi.common.entity.EntitySpellProjectile.func_70184_a(EntitySpellProjectile.java:183)
at net.minecraft.entity.projectile.EntityThrowable.func_70071_h_(SourceFile:204)
at vazkii.psi.common.entity.EntitySpellProjectile.func_70071_h_(EntitySpellProjectile.java:128)
at net.minecraft.world.World.func_72866_a(World.java:1862)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:699)
at net.minecraft.world.World.func_72870_g(World.java:1831)
at net.minecraft.world.World.func_72939_s(World.java:1663)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:544)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:701)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:344)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:605)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:481)
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 vazkii.psi.api.internal.Vector3.(Vector3.java:62)
at vazkii.psi.common.spell.operator.vector.PieceOperatorVectorRaycast.raycast(PieceOperatorVectorRaycast.java:70)
at vazkii.psi.common.spell.operator.entity.PieceOperatorFocusedEntity.getEntityLookedAt(PieceOperatorFocusedEntity.java:60)
at vazkii.psi.common.spell.operator.entity.PieceOperatorFocusedEntity.execute(PieceOperatorFocusedEntity.java:48)
at vazkii.psi.api.spell.CompiledSpell$Action.execute(CompiledSpell.java:95)
at vazkii.psi.api.spell.CompiledSpell.execute(CompiledSpell.java:51)
at vazkii.psi.api.spell.CompiledSpell.safeExecute(CompiledSpell.java:70)
at vazkii.psi.common.entity.EntitySpellProjectile.cast(EntitySpellProjectile.java:211)
at vazkii.psi.common.entity.EntitySpellProjectile.cast(EntitySpellProjectile.java:187)
at vazkii.psi.common.entity.EntitySpellProjectile.func_70184_a(EntitySpellProjectile.java:183)
at net.minecraft.entity.projectile.EntityThrowable.func_70071_h_(SourceFile:204)
at vazkii.psi.common.entity.EntitySpellProjectile.func_70071_h_(EntitySpellProjectile.java:128)
at net.minecraft.world.World.func_72866_a(World.java:1862)
at net.minecraft.world.WorldServer.func_72866_a(WorldServer.java:699)
at net.minecraft.world.World.func_72870_g(World.java:1831)

-- Entity being ticked --
Details:
Entity Type: Psi.psi:spellProjectile (vazkii.psi.common.entity.EntitySpellProjectile)
Entity ID: 2828
Entity Name: entity.Psi.psi:spellProjectile.name
Entity's Exact location: 233.13, 82.46, 989.45
Entity's Block location: 233.00,82.00,989.00 - World: (233,82,989), Chunk: (at 9,5,13 in 14,61; contains blocks 224,0,976 to 239,255,991), Region: (0,1; contains chunks 0,32 to 31,63, blocks 0,0,512 to 511,255,1023)
Entity's Momentum: -1.85, -1.00, 0.47
Entity's Rider: ERROR NullPointerException: null
Entity's Vehicle: ERROR NullPointerException: null
Stacktrace:
at net.minecraft.world.World.func_72939_s(World.java:1663)
at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:544)

-- Affected level --
Details:
Level name: world
All players: 1 total; [EntityPlayerMP['sanaradain'/2827, l='world', x=238.83, y=84.00, z=988.18]]
Chunk stats: ServerChunkCache: 1067 Drop: 0
Level seed: -4241746115136290137
Level generator: ID 00 - default, ver 1. Features enabled: true
Level generator options:
Level spawn location: -28.00,64.00,256.00 - World: (-28,64,256), Chunk: (at 4,4,0 in -2,16; contains blocks -32,0,256 to -17,255,271), Region: (-1,0; contains chunks -32,0 to -1,31, blocks -512,0,0 to -1,255,511)
Level time: 3452190 game time, 2919767 day time
Level dimension: 0
Level storage version: 0x04ABD - Anvil
Level weather: Rain time: 27753 (now: false), thunder time: 111556 (now: false)
Level game mode: Game mode: survival (ID 0). Hardcore: false. Cheats: false
Stacktrace:
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:701)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:344)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:605)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:481)
at java.lang.Thread.run(Thread.java:745)

-- System Details --
Details:
Minecraft Version: 1.8.9
Operating System: Linux (amd64) version 3.14.32-xxxx-grs-ipv6-64
Java Version: 1.8.0_72, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 4307232656 bytes (4107 MB) / 5195169792 bytes (4954 MB) up to 5195169792 bytes (4954 MB)
JVM Flags: 3 total; -Xmx5120M -Xms5120M -Xss2M
IntCache: cache: 0, tcache: 0, allocated: 12, tallocated: 96
FML: MCP 9.19 Powered by Forge 11.15.1.1757 71 mods loaded, 71 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCHIJAAAA mcp{9.19} Minecraft Coder Pack
UCHIJAAAA FML{8.0.99.99} Forge Mod Loader
UCHIJAAAA Forge{11.15.1.1757} Minecraft Forge
UCHIJAAAA Baubles{1.1.3.0} Baubles
UCHIJAAAA aura{591} Aura Cascade
UCHIJAAAA bagginses{2.1.5b} Bagginses
UCHIJAAAA BetterAchievements{0.1.1} Better Achievements
UCHIJAAAA BloodMagic{1.8.9-2.0.0-253-ss} Blood Magic: Alchemical Wizardry
UCHIJAAAA bookshelfapi{2.3.2} Bookshelf
UCHIJAAAA Thaumcraft{5.1.6} Thaumcraft
UCHIJAAAA Botania{r1.8-249} Botania
UCHIJAAAA BuildCraft|Core{7.2.0-pre12} BuildCraft
UCHIJAAAA BuildCraft|Transport{7.2.0-pre12} BC Transport
UCHIJAAAA BuildCraft|Energy{7.2.0-pre12} BC Energy
UCHIJAAAA BuildCraft|Factory{7.2.0-pre12} BC Factory
UCHIJAAAA BuildCraft|Silicon{7.2.0-pre12} BC Silicon
UCHIJAAAA BuildCraft|Robotics{7.2.0-pre12} BC Robotics
UCHIJAAAA BuildCraft|Builders{7.2.0-pre12} BC Builders
UCHIJAAAA buildingbrickscompatvanilla{1.8.9-1.3.2} Building Bricks Vanilla Compat
UCHIJAAAA buildingbricks{1.8.9-1.3.2} Building Bricks
UCHIJAAAA Chameleon{1.8.9-0.2.1} Chameleon
UCHIJAAAA mcmultipart{1.0.7} MCMultiPart
UCHIJAAAA CharsetLib{0.2.1} ‽
UCHIJAAAA CharsetTweaks{0.2.1} *
UCHIJAAAA CharsetWires{0.2.1} +
UCHIJAAAA CharsetAudio{0.2.1} ♫
UCHIJAAAA CharsetStorage{0.2.1} #
UCHIJAAAA CharsetPipes{0.2.1} |
UCHIJAAAA CharsetGates{0.2.1} &
UCHIJAAAA chisel{@Version@} Chisel
UCHIJAAAA chiselsandbits{mc1.8.9-v1.8.11} Chisels & Bits
UCHIJAAAA compasscoords{1.8.9-0.2.6} Compass Co-ords
UCHIJAAAA ComputerCraft{1.78} ComputerCraft
UCHIJAAAA craftingtweaks{3.0.51} Crafting Tweaks
UCHIJAAAA crafttweaker{3.0.0} crafttweaker
UCHIJAAAA dsurround{2.0.4.10} Dynamic Surroundings
UCHIJAAAA ShetiPhianCore{3.1.0} ShetiPhian-Core
UCHIJAAAA EnderTanks{1.2.1} EnderTanks
UCHIJAAAA ezstorage{1.0} EZ Storage
UCHIJAAAA fastleafdecay{1.6} Fast Leaf Decay
UCHIJAAAA flatcoloredblocks{mc1.8.9-v1.7} Flat Colored Blocks
UCHIJAAAA Waila{1.6.0} Waila
UCHIJAAAA FTBL{2.0.2} FTBLib
UCHIJAAAA FTBU{2.0.2} FTBUtilities
UCHIJAAAA furnus{1.7} Furnus
UCHIJAAAA graves{1.8.9-b41-universal} Graves Mod
UCHIJAAAA hopperducts{1.4.6} Hopper Ducts
UCHIJAAAA k4lib{1.8.9-1.0.16} K4Lib
UCHIJAAAA HydCraft{1.8.9-3.1.65} Hydraulicraft
UCHIJAAAA IGWMod{1.2.4-4} In-Game wiki Mod
UCHIJAAAA intangible{0.0.23} Intangible
UCHIJAAAA inventorysorter{0.7.4+26} Simple Inventory sorting
UCHIJAAAA IronChest{6.0.125.770} Iron Chest
UCHIJAAAA JEI{2.28.2.166} Just Enough Items
UCHIJAAAA journeymap{5.1.3} JourneyMap
UCHIJAAAA mantle{1.8.9-0.8.jenkins92} Mantle
UCHIJAAAA testdummy{1.0} MmmMmmMmmMmm
UCHIJAAAA Morpheus{1.8.9-2.0.58} Morpheus
UCHIJAAAA neotech{2.3.7} NeoTech
UCHIJAAAA fodc{1.7.2} Ore Dictionary Converter
UCHIJAAAA playerrugs{0.0.1} Player Rugs
UCHIJAAAA PneumaticCraft{1.13.7-11} PneumaticCraft
UCHIJAAAA progressiveautomation{1.6.35} Progressive Automation
UCHIJAAAA Psi{beta-16} Psi
UCHIJAAAA RandomThings{3.6.2} Random Things
UCHIJAAAA rftools{4.22beta25} RFTools
UCHIJAAAA simpleretrogen{2.2.2+3} Simple Retrogen
UCHIJAAAA StorageDrawers{1.8.9-2.4.1} Storage Drawers
UCHIJAAAA tconstruct{1.8.9-2.1.0.jenkins101} Tinkers' Construct
UCHIJAAAA thaumicinfusion{4.82} Thaumic Infusion
UCHIJAAAA wawla{1.4.7} What Are We Looking At
Loaded coremods (and transformers):
NowWithRendering (hopperducts-mc1.8.8-1.4.6.jar)
net.fybertech.nwr.NowWithRendering
LoadingPlugin (RandomThings-MC1.8.9-3.6.2.jar)
lumien.randomthings.asm.ClassTransformer
thaumicinfusion (ThaumicInfusion-1.8.9-4.82.jar)
drunkmafia.thaumicinfusion.common.asm.BlockTransformer
drunkmafia.thaumicinfusion.common.asm.WorldTransformer
ThaumcraftLoader (Thaumcraft-1.8.9-5.1.6.jar)

FldLoadingPlugin (FastLeafDecay-1.8-1.6.jar)
com.olafski.fastleafdecay.FldTransformer
dsurroundcore (DynamicSurroundings-1.8.9-2.0.4.10.jar)
org.blockartistry.mod.DynSurround.asm.Transformer
Pulsar/tconstruct loaded Pulses:
- TinkerCommons (Enabled/Forced)
- TinkerWorld (Enabled/Not Forced)
- TinkerTools (Enabled/Not Forced)
- TinkerSmeltery (Enabled/Not Forced)
- TinkerGadgets (Enabled/Not Forced)
- TinkerOredict (Enabled/Forced)
- TinkerIntegration (Enabled/Forced)
- TinkerFluids (Enabled/Forced)
- TinkerMaterials (Enabled/Forced)
- chiselsandbitsIntegration (Enabled/Not Forced)
- TinkerDebug (Enabled/Not Forced)

Profiler Position: N/A (disabled)
Player Count: 1 / 60; [EntityPlayerMP['sanaradain'/2827, l='world', x=238.83, y=84.00, z=988.18]]
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)

Fixed with 2af07a0.
Use Selector: Attacked Entity next time.