A year late but… I think he should be typed as a Centaur Minotaur Warrior, be made Black/Red, and his casting cost should be BBBRRR

@FanOfMostEverything  
Darn Textile formatting. That should be plus 1/plus 1 counter.

Super-Malignus? For the exact same cost? Yeah, no.
 
May as well add my version:
 
Tirek, Soul Stealer BBB  
Legendary Creature — Demon  
Whenever another creature dies, put a +1/+1 counter on Tirek, Soul Stealer.  
BBB, T: Destroy target creature with power less than Tirek’s power.  
0/3

@DMPony  
You’re darn right they still do multicolor cards. Several comparatively recent sets are centrally based around the idea. ^_ ^
 
For example, there’s the Ravnica block, which is all about two-color combos (Flavor-wise, the world of ravnica has ten guilds, each of which is based around two of the five colors).

I also made an MTG Tirek: http://www.tradecardsonline.com/im/selectCard/card_id/63844/goal/DC
 
Like in the show, mine starts out underwhelming but can get out of control very quickly. I’m thinking of making a Discord to accompany it with a “target creature fights another target creature” effect.

Seems he should also be a Black/Red dual-color (do they even still do those? I quit MTG way the hell back in the Urza series…)
 
I’d go with something like:  
3 colorless 1 black 1 red  
Lord Tirek comes into play with one + 1/+ 1 counter and has a base of 0/0  
2 black:2 red (or 1/1 and 2 colorless?) = add X -1/-1 counters to target creature and add that many + 1/+ 1 counters to Lord Tirek, where X is equal to the number of + 1/+ 1 counters already on Lord Tirek
 
And possibly a fireball effect to remove X + 1/+ 1 counters to deal damage to creatures or players
 
/shrug, I haven’t played MTG in too long, still fun to think about. My friends and I used to print out custom cards just for kicks all the time.

@LanceOmikron
 
Sneak-Attack then Fling for good measure.

should be classed as a centaur-deamon

Yeah, that makes sense. Keeping it as-is makes it another Emrakul, and that would be a nightmare to play against.

@Background Pony #7F26  
I get the feeling that the first ability should be worded as something like this:
 
“When you cast Lord Tirek, all creatures lose all abilities. Tirek enters the battlefield with a + 1/+1 counter on it for each creature that lost an ability this way.”
 
Otherwise, that enormous mana cost would be meaningless. Folks would never pay it, and instead would exclusively just use methods to get around it (stuff like Elvish Piper).

I thought of what mechanics I’d like for him, but they also are kind of overpowered. For what I want to do, he’d have to be in the realm of 12 mana or so. I guess it kind of fits, since when he’s powered up he’s almost a god.
 
Cost: 8UBBR
 
Legend - Centaur Demon
 
Power/Toughness: 1/1
 
Abilities Text:
 
Shroud.
 
When Lord Tirek enters the battlefield, all creatures lose all abilities. For each creature that lost an ability, put a + 1/+1 counter on Tirek.
 
If Tirek has 7 or more + 1/+1 counters, he is indestructible.
 
1UU: Counter target spell and put a + 1/+1 counter on Tirek.
 
UBR: Target creature loses all abilities, then put a + 1/+1 counter on Tirek.

This should cost way more. At least 10 mana.

I don’t care if it’s been mentioned twice here already. A fucking five Mana cost for something this overwhelming? That’d be a batshit banana sundae even without the addition of his last ability, keeping his damage from being prevented.
 
However, with that said… where can I get one? Or three?

Damn, that’s OP.

Only five mana for that? I get the sense that that’s a teensy bit overpowered. Just put it in a red/blue deck that can easily grant haste and unblockability, and your opponent is toast.

I think he should start as 1/1 and have a mechanics for adding +1/+1 tokens

Wayyyyy undercosted, even for a mythic rare (which are OP as a rule)