Originally Posted by
Eroginous
The reason why tribal decks aren't a very strong deck type is the same reason why building a deck around one theme (like burn spells, discard spells, life gain, ect), are not strong deck types. Every deck needs multiple win conditions and versatility. Tribal decks tend to focus on creature synergy and not really much else. There have been exceptions in the past, such as elves, goblins, and slivers, but for the most part, you want to pick an actual deck archetype to build, and only use creatures that work well in it.
For instance, if your tribal deck is supposed to be a stompy aggro deck, then you should cut out a lot of the creatures and replace them with spot removal and other tempo cards.