Believe it or not, treecko don’t often need toys. Certainly, they’ll play with toys you give your other pokémon (although as a word of advice, due to their shedding skin and the fact that they often carry salmonella, you perhaps will want to give them toys that are easy to clean), but oftentimes, treecko will be content to sun, climb, and train.
That said, above all else, it’s important to provide your treecko with an optimal environment. They’re reptiles, grass-type tropical ones at that, and that means they need plenty of sunlight, warmth, and humidity. (Because of their grass typing, they are not nocturnal, by the way, unlike their animal “counterparts.”) If you live in an urban environment and/or can’t provide your treecko with at least eight hours of sunlight, you’ll need to provide them with a heat lamp, particularly one that can emit UVA and UVB lighting. This will become especially important as your treecko evolves and develops more plant-like characteristics, as by then, it will need light that mimics sunlight to photosynthesize.
Regardless of whether or not you will require a heat lamp, your treecko’s environment will also need two key features: a flat rock on which they can sun (or hide beneath, if they choose) and something they can climb. For the latter, a tree would be ideal, but a cat tree (typically used by meowth, skitty, espurr, and litten trainers as a scratching post) will do just as well. Treecko will often use the former to rest while sunning, and the latter is simply for comfort.
Likewise, to mimic humidity and to keep your treecko’s skin moist on dry days, invest in a humidifier to add moisture to the air at a constant rate. Alternatively, on especially warm days, you may also spray the air periodically with a bottle of clean water.
As your treecko evolves, it will of course be imperative that you provide more and more space for it. While it’s possible to continue keeping a grovyle indoors, it’s highly inadvisable to keep a sceptile due to its sun and space requirements. Thus, it’s worth it to invest in an everstone early on—preferably at the treecko stage—if you live in an urban environment with limited space. If you cannot provide your sceptile with adequate room to sun and climb, you may wish to consider rehoming it or making arrangements with your landlord to provide rooftop accommodations for it.
Despite being able to photosynthesize in later stages, members of the treecko line are actually carnivores and prefer insects—particularly live ones. (This is why many treecko trainers prefer feeding their pokémon kibble, actually. It’s either less of a hassle, or the trainer isn’t particularly inclined to handle live crickets and mealworms.) They can eat berries or leafy greens, and their later stages can gather energy from photosynthesizing, but keep in mind that neither of these methods should be their primary diets due to their nutritional requirements (contrary to popular belief). Either way, provide your treecko with clean water and change their water bowls at least once a day. Twice for later stages.
Regarding keeping treecko’s environment clean, treecko can be taught to use a litter box, but be sure to line it with bark, not sand, as sand carries a risk of soaking up precious humidity. Be sure to clean not only the litter box but your treecko’s environment (unless it lives outside, of course) regularly as, once again, treecko skin may carry salmonella.
Incidentally, treecko do indeed shed their skins (as do their later stages, although sceptile do so at a less frequent rate), but it’s not necessary to clean it up, as the first thing treecko will do upon shedding is eat their own skin. (It’s a defense mechanism held over from their time in the wild, not to mention the skin is a ready source of energy.) You’ll be able to tell if your treecko is about to shed based on energy levels and color: if it seems dull in color and isn’t quite as energetic during your training sessions, then you’ll know. Provide your treecko with an especially humid environment during this time and keep an eye on its extremities. If It seems like its skin is not coming off its toes or limbs, wrap it with wet towels for at least a half an hour. If this doesn’t help, use a pair of clean tweezers to gently peel the skin off for your treecko.
Finally, as always with tamed pokémon, you’ll want to exercise your treecko daily by putting it through at least a half an hour of training. No bedding is required for sleep, as most treecko prefer to sleep in trees or whatever else they can climb.