Based on patterns in previous Tales of Arcadia, here’s a list of what I think is likely to happen in Wizards Season 1. I like the Bingo card format but I find my guesses tend to be too wordy to be legible on the actual Bingo cards.
1) The talking cat wearing glasses will be a Siamese. All cats onscreen in ‘Tales of Arcadia’ so far have been Siameses.
2) Arcadia Oaks Academy will finally be an onscreen setting.
4) More Arthurian references.
5) Time Magic. Trollhunters Season 1 had time-stopping with the Kairosect in It’s About Time, and 3Below Season 1 had time-loops in D’Aja Vu.
6) Season 1 of Wizards will overlap with the most recently-released season of 3Below - meaning, if there hasn’t been Season 2 of 3Below yet, it will also overlap with Season 3 of Trollhunters. (My other theory is that it starts pre-Trollhunters Season 1, but that feels less likely.)
7) Shiny/glittery animation.
8) That one guy whose name I can never quite catch (Douce? Douxie? the one who invited Claire to the Battle of the Bands, and was a waiter, and used a guitar to take down a Gumm-Gumm) and his band are the protagonists.
10) An actual dragon. There have been dragon-like characters - the Stalkling and Buster - already, but let’s see an identified-as-such dragon.
11) Significant use of the colour blue, previously used for the Amulet of Daylight in Trollhunters and Akiridion tech in 3Below.
12) A power-struggle not connected to the other two series. General Morando was not relevant to Trollhunters, and Gunmar was only tangentially related to events in 3Below.
14) Fun new curse word, like ‘bushigal’ from Trollhunters and ‘kleb’ from 3Below.
15) Running joke on a series-specific branch of crude humour. Trollhunters had dick jokes, mostly related to Rule Number Three, and 3Below had poop and fart jokes mostly revolving around Luug.
16) Flashback sequences, possibly related to the time magic shenanigans previously speculated, of events centuries prior.
17) More magic rocks. Maybe Jim finally gets the sunlight-immunity stone for the Amulet, or we find out what the blue stone in the Amulet is.
18) Magician Toby! Toby’s interest in magic (which Trollhunters more or less dropped after Season 1 so the magic arcs could focus on Claire) is readdressed.
19) Obligatory Hetero Romance Arc for one of the new teenage protagonists. (For the record, I think Jlaire and Staja are cute; this is a prediction based on a trend, not a judgement of it.)
20) First name revealed for Coach Lawrence and/or Señor Uhl.
21) An attempt to make Merlin a more sympathetic character, either so it will feel like a twist instead of an obligatory when he’s confirmed as the Big Bad or to set up for a genuine redemption arc. (Obviously they’ll want to keep it ambiguous in the first season.)
22) Ley lines, based on an interview regarding why strange things seem drawn to Arcadia. (”Why Arcadia? What is it about this town that makes it a ley line for all this activity?” “It's funny you should mention that. That is something that we've always talked about in terms of intersectional ley lines. In fact, when Guillermo first pitched this idea that there's all these things happening in this one town, he said ley lines very specifically.” Den of Geek interviewing Marc Guggenheim about 3Below.)
23) Non-human disguised as human via shapeshifting or illusion magic.
24) Crossover episode with events of one or both previous Tales of Arcadia series seen from Wizards characters’ perspective.
25) Someone pulls a Heroic Sacrifice in the first season finale. AAARRRGGHH saved Toby in the Season 1 finale of Trollhunters and temporarily died, and Vex attacked the bounty hunter in the Season 1 finale of 3Below and got captured.