It's an all black adult sizes tee with Green Hill Zone theme. You can literally see 'around the world' of this tiny sphere area. Circling it, you can see flying Tails, running Sonic, jumping Knuckles & Eggman in his Egg o Matic, along with various level staples like rings and palm trees. The classic logo is at the bottom, and everything's 16 bit look / pixelated.
This shirt may be associated with Sonic Mania, it appears when the first Mania items were released.
Christmas / Holiday season 2016 brought in a "Christmas craze" of items.
For whatever reason, 2016 is the first year that it seems that "Holiday Sonic" really started being pushed with wear-able merchandise. This "Caroling Tee" is one of the first items. It has new art for neoclassic Tails & Sonic. They're shown holding books of lyrics and singing. Little colored music notes surround them & they're also drawn with winter wear like a little scarf. Tails has his eyes closed. The shirt itself is plain & green.
The neoclassic art here is good, it resembles older Japan art of Tails where he's actually correct. What's unusual is that this has to be 1-off art. Unlike most stock art items (or tees!) the art is generally meant to be used "all-purpose" but this one has only 1: Songs. Maybe its a little out of place? CAN Sonic sing? Still, it's an interesting effort item.
Unlike the others above (also released for Mania) This tee is directly Sonic Mania. It MAY be limited edition. The plain green tee has the Sonic Mania logo printed large in the middle, in black. There are little solid-color fill graphics for running Tails, Sonic & gliding Knuckles going over the logo. Do note that the logo here has 'weathering' that crackly 'faux wear' that makes the design look a big shabby/aged on purpose.The little characters don't have the weathering, though.
This is the first known Mania logo tee & was released late 2016.
This navy blue tee is called the Genesis Spirit Shirt
It has weathered white paint for its only design color. The rectangle design is a sort of collage of nostalgic type Sonic items/images. There are geometric shapes, an old-type monitor-like shape at the top (with sihlouette running Sonic in it) a row of rings, laying-down-waiting Sonic (from Sonic CD) & the bottom has the line work for the old Genesis system.
It's quite a classic-homage type shirt, and was released for Sonic Mania in late 2016.
Here's a Halloween themed tee!
This one is a bit of a mystery, too. It was only for sale on Amazon, and only for a short time. However, instead of going into 'sold out' status, it simply disappeared off of everywhere without a trace. Notice that it has the same blank, white long-rectangle shaped tag as all of these new seemingly "amazon only" tees on this page.
The design brings in another piece of new neoclassic art, this time with 'ready to run' Sonic looking up/aggrivated. Eggman in his Egg o Matic is looming in front of a full moon, with Batbrain badnick robots in sihloutte flying all around as well. He's dressed for Halloween too, as he's wearing a big black/red cape. The slogan on the tee is "I'll Get You Sonic" spelled out in a blocky red font. It's an interesting tee...if anyone was able to buy it.
This classic style tee has some instructions, illustrated by Sonic!
This tee's slogan is "How to be Awesome!" which is written at the top over 4 panels, each with a different classic stock Sonic. The first has running Sonic with "Bring the speed", the second has forward-facing with "bring the attitude", the third has finger-waving with "Bring the cool" and the last has the less-common football-catching with "bring your "A" game".
This shirt is a lot wordier than others, but, it is good advice & makes it stand out. It looks like a little-kids size, but where is it sold? This is a 2017 release by BioWorld.
This shirt is called "Men's Pixel Sonic Run".
It's similar to the earlier "Men's Pixel Punk", but uses a different overly-large sprite with 16 bit look. The logo is big, classic, and unpixelated. This has the general running fast Sonic, complete with the 'sweep' sort of effect going on with his curving shoes. Because the shirt itself is white, the socks sort of get a little lost in the desgin. This MAY be a dual-country release item. If it is, it would also appear in the UK area somewhere. It is suspected to be a 2016 release. But where was it found?
This shirt is called "Name Pose Stars Tee".
It's an all black teens/boys size shirt found at Wal Mart in spring/summer 2017. The background 'sunburst' shape is done in silver-tone ink. The little retro-style asterisk-type 'stars' are in white ink, as is Sonic's name in script. This also tries to look retro by only using blue, black & white for Sonic, which means he has blue shoes as well. The pose is the one introduced around Sonic CD era (may be a bit of a neoclassic re-work?) which wasn't as frequently used, which helps keep this fresher looking. If you can find this, it shouldn't be too expensive.
This is a fun tee!
Neo-classic line art is used to spice up Classic Sonic & Tails all over this blue-gray shirt. It has Sonic & Tails in full color in the winged ring, just like on the title screen of Sonic 2. But, the 'background' of the tee is a bunch of black line-only stock arts. You can see the "Sonic & Tails sits on the star", Eggman, laying/yawn Sonic, & numerous other little fun stocks. The mystery is, where is this sold? There were reports of Amazon, but no real consistent way to find it. Write in if you've found this shirt for credit.
During the 'ugly Christmas sweater trend' of 2016, these tees appeared. They're meant to resemble 'sweater stitching' with a sort of pixelated look & simplified designs. If it was too hot for sweaters, this imitating tee could work instead. It's got neo classic finger waving Sonic, rows of snowflakes, rings & emeralds in the background. A red shirt was made, which makes sense, but why a black one? It spoils the point of trying to 'look like' or 'remind of' a tacky sweater.