Spear of the magus vs obsidian shard for Janus.
TL;DR: Spear is better then obsidian shard. Lategame full build, Spear without stacks and obsidian shard are Equal~


Level 14 vs mages, 1+2+Passive
-Vamp,Lost Artifact,Pen boots,Obsidian shard
Portal:		367*(100/110)	=334
Passive:	36*(100/110)	=32
Unstable vortex:431*(100/110)	=392
Double tap:	129*(100/110)	=117
Total:				=875
-Vamp,Lost Artifact,Pen boots,Spear
Portal:		349*(100/105)	=332
Passive:	34		=35
Unstable vortex:410		=410
Double tap:	123		=123
Total:				=900

-Spear is 2.8% more damage


Level 14 vs the rest, 1+2+Passive
-Vamp,Lost Artifact,Pen boots,Obsidian shard
Portal:		367*(100/119)	=308
Passive:	36*(100/119)	=30
Unstable vortex:431*(100/119)	=362
Double tap:	129*(100/119)	=108
Total:				=808
-Vamp,Lost Artifact,Pen boots,Spear
Portal:		349*(100/119)	=293
Passive:	34*(100/104)	=33
Unstable vortex:410		=410
Double tap:	123		=123
Total:				=859

-Spear is 6.3% more damage

Level 20 vs mages, 1+2+Passive
-Toth,Chronos,Boots,Obsidian,Soulreaver,Rod
Portal:		703*(100/110)	=639
Passive:	176*(100/110)	=160
Unstable vortex:824*(100/110)	=749
Double tap:	247*(100/110)	=224
Total:				=1772 + soulreaver proc
-Toth,Chronos,Boots,Spear,Soulreaver,Rod
Portal:		681*(100/105)	=648
Passive:	167		=167
Unstable vortex:799		=799
Double tap:	240		=240
Total:				=1854 + soulreaver proc

-Spear is 4.6% more damage

Level 20 vs the rest, 1+2+Passive
-Toth,Chronos,Boots,Obsidian,Soulreaver,Rod
Portal:		703*(100/124)	=567
Passive:	176*(100/124)	=142
Unstable vortex:824*(100/124)	=664
Double tap:	247*(100/124)	=199
-Total:				=1572 + soulreaver proc
-Toth,Chronos,Boots,Spear,Soulreaver,Rod
Portal:		681*(100/125)	=544
Passive:	167*(100/110)	=151
Unstable vortex:799		=799
Double tap:	240		=240
Total:				=1734 + soulreaver proc

-Spear is 10.3% more damage


Level 14 vs mages, 2+passive
-Vamp,Lost Artifact,Boots,Obsidian:
Unstable vortex: 431*(100/110)=391
Passive:	 36*(100/110) =32
Total:			      =423
-Vamp,Lost Artifact,Boots,Spear:
Unstable vortex: 410*(100/105)=390
Passive:	 36	      =36
Total:			      =426

-Spear is 3 points more damage.

Level 14 vs the rest, 2+passive
-Vamp,Lost Artifact,Boots,Obsidian:
Unstable vortex: 431*(100/119)=362
Passive:	 36*(100/119) =30
Total:			      =392
-Vamp,Lost Artifact,Boots,Spear:
Unstable vortex: 411*(100/119)=345
Passive:	 36*(100/104) =34
Total:			      =379

Obsidian is 13 points more damage.

Level 20 vs mages, 2+passive
-Toth,chronos,Boots,Obsidian,Rod,Soulreaver:
Unstable vortex: 431*(100/110)=391
Passive:	 36*(100/110) =32
Total:			      =423
-Toth,chronos,Boots,Spear,Rod,Soulreaver:
Unstable vortex: 410*(100/105)=390
Passive:	 36	      =36
Total:			      =426 + soulreaver proc

-Spear is 3 points more damage.

Level 20 vs the rest, 2+passive
-Toth,chronos,Boots,Obsidian,Rod,Soulreaver:
Unstable vortex:824*(100/124) =664
Passive:	176*(100/124) =142
Total:			      =806
-Toth,chronos,Boots,Spear,Rod,Soulreaver:
Unstable vortex:799*(100/125) =639
Passive:	167*(100/110) =151
Total:			      =790 + soulreaver proc

Obsidian is 16 points more damage.