I need some suggestions for my strategy game.

Maybe different colors.. each 'magi-tile' ups your creature one level, but each can benifit from each color once. So although you can funnel your entire army over that little yellow square, standing on it does you no good. This way you could put some of the 'higher' colored squares in a contested area to encourage conflict.

How are you denoting a level of a creature?

SO what you are saying is that there is a Swordman entity (card, figure whatever).. whose level is based what he is currently carrying. And the mage is of a certain level based on what is in his book. So if I understand this right, steping on magi-tile basically allows me to draw a specific type of card. So a swordsman isn't really gaining experience, he is picking up stuff.
Or do I have this backwards somehow?

Well depending on your theme the colors could be linked to elements.. a red square is a fire-y thing. If the level of a creature is really just the stack of his cards, then picking up more cards automatically raises his level. You just prevent him from carrying more than one of each color.

Who knows maybe I misunderstand your description.

Ok, but in an odd way skills and specials are still an inventory. My ThingfromtheBlackLagoon is carrying the knowledge (and the card) to do something just like my swordsman is carrying his sword. Is that the rule though, that level is determined by the cumulative of the cards stacked beneath an entity (regardless of type). If so, how do you gain skills, specials? And are they like cards or assigned somehow?

Well now, that is a possibility. There are ways you could go about making that work without totally imbalancing the game with god-like super-units. The strategy/war game I am working on now has something like this mechanic for developing planets. Each turn you can develop a planet one point, with the max being six points. But for the development to be successful you must roll a dice with a value HIGHER than the current development. Even though you can invest resources to roll more dice, the odds of success decrease as the system develops to a greater level. Result - players must economize to some extent, developing all of their planets to varying degrees.

Now, if I understand your game at all, this particular solution won't help. If "levels" are cards in your game, then there could be a foil to over-inflating a single fighter. Maybe high-level units are slower, or have less "initiative", or something. Maybe each of those "levels" are specific powers and the player must choose only one for a turn - so a small unit is not so dwarfed in a battle. Maybe every blue moon a player has a chance to strike down lightning from the heavens and obliterate a single fighter - now that would discourage putting all your eggs in one basket! Or one of the powers is the "Kingslayer", which gives a character the power to kill larger fighters, regardless of their size. Just brainstorming, but as you can see the possibilities are endless.

Speaking of which, has anyone ever tried arranging cards with every other row shifted up or down 1/2 a card? The result is that each card has six cards adjacent - exactly like a hex board! I bring this up because I had this revelation when I was designing a "Jungle Adventure" tile exploration game. Squares are MUCH easier to cut with scissors than hexes. I notice that the internet game "Bookworm" uses this mechanism of arranging tiles.