Thing is, surprise attacks might be a bit tricky to pull off, because if these robots are huge, then how can they sneak up

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I would have certain tiles that can spawn enemies, like a forest block on your hex grid might have an enemy hiding in it, or a cave block, or something like that. Anyway, you could scan the whole map, and if there's a hiding robot, and the areas next to it have been revealed by the player, then the robot should move and start attacking the player. I'm guessing you'll have some sort of fog of war? - well I'd use that to decide if the enemy reveals itself. Also, I would have hiding enemies move around their hiding places - a cluster of forest blocks for instance, the enemy could move around these randomly, but staying within the forest. Then the player might reveal one side of the forest, and the enemy might not know yet because they are on the opposite side - when they get around to the revealed part, they can pick up the scent.
For actual combat, I would say that just having a portrait of the enemy would be fine, some attack and defend options, but a straightforward system, no movement or complex attacks that the player might not be interested in. I would just have a portrait with the stats underneath, and some big, bold attack options - maybe add on layers of strategy with that. For example, have a weak, medium, and strong attack and limit the attack that the player can do - if they do weak attacks then their limit increases, the more weak attacks means they have extra power to pull off strong attacks, and have the medium attacks remain consistant. Maybe a little like battle XP - if you do a really good attack, then give extra power, or even have a battery that the player can use, instead of attacking they save their power for the next round. Turn based combat is ideal for this type of game I think - let the player take their time and strategise. Never fall into the Final Fantasy trap, and have trully random encounters - you should always be able to clear out all the enemies, otherwise it becomes tedious, feels like you aren't getting anywhere. You can always let the weaker enemies re-spawn after some time, so sand boxing an area after completing it still holds surprises, but nothing the player can't deal with.
Lastly, I have to ask why it has to be Zoids - doing that will limit what you can do with your game, might be worth considering taking the project a different route 0 like invent your own robots and plot, take ownership - Zoids fans will like it because it would be inspired by Zoids, but then you won't have any copyright nonsense to deal with, and you'll have a much more personal game.

Health, Ammo, and bacon and eggs!
