What are two games you could never envision possibly having their mechanics fused. - To be clear on what I mean about that "Pokemon Snap" and "Gears of War" are not an example because mechanically they, put together, end up with an arcade shooter that has puzzle elements DESPITE being so stylistically alien to each other. Same thing with New Super Mario Bros and Assassin's Creed, you'd essentially have a 2D stealth platformer with RPG elements and power-ups.

Lets say Animal Crossing meets CoD.

Need for Speed + CoD = Twisted Metal? :P

I'll make an alarm on my phone to remind me to look up a Lets Play when I get home, sounds like an interesting fusion if accurate.

On the topic of ones we can't envision happening that seem to have happened / are happening anyway - Gears of War + Fire-Emblem sounds insane to me and yet, Project S.T.E.A.M. is a thing.

Tetris + Age of Empires. How do you even start with those?

isn't that more 'Rage' then?

Actually 'where to start' is the reason why I'm asking. I'm trying to get my creative juices flowing for it.

My immediate thought for that fusion is a game where you control a space colony and keep getting sent random 'building/compartment' modules, which reload every two minutes (causing you to lose the chance to use the current one if you haven't yet). Where you add these modules in relation to the rest of your colony modifies some of the details of exactly what they do. You don't get to control what your inhabitants do, but you do get little text inputs explaining what your politicians are feeling and thus warning you how they might react to different upgrades.

Obviously lining-up certain types of upgrades could have significant boons. I think the most obvious Tetris and Age of Empires touches would be having them develop the ability them change colony development stages and start being sent a wider range of modules at increased speed with every age. Image keeping track of all that while monitoring your opponents behavioural trends.

Something similar to the StarJeweled minigame from Starcraft 2?

Virtues Last Reward + Halo

I am afraid I've not played it, and your image is showing to me a large text image  statement saying:

Sorry, hotlinking images is not allowed.
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how about uncharted meets tomb raider