Don't run Thoughtseize against other aggro decks. It's a horrendous topdeck lategame and not as useful as a kill spell or another creature early game most of the time.

Why not Athreos, God of Passage? It can be great in this sort of deck. For example, Athreos, God of Passage + Bloodsoaked Champion . If they choose to pay 3 to have the Champion go to the grave, you can bring it back for after you attacked. If they don't pay the life, it just goes right back into your hand which you can just pay ! It's a win-win.

@SirFowler: You know I did have my Athreos mainboarded originally, but switched it out post-DTK.. However, I only own 1x copy of Athreos, God of Passage, so what should the other Citadel Siege be? A Gravepurge(recursion/draw), Sign in Blood(draw/game-ending Shock), or... maybe even a Blood-Chin Fanatic?!

Secure the Wastes or more creatures

Here's what I would take out

1 Thoughtseize for 1 Blood-Chin Fanatic

1 Citadel Siege for 1 Sign in Blood or Read the Bones. Read the Bones is better in multi-colored decks because the mana fixing can get kind of difficult at times.

The other Citadel Siege for 1 Palace Siege

Palace Siege is a multi-tool that can help end-game better than Sign in Blood because it happens every turn. It can also help with graveyard recursion if needed.