Not that surprising that Tristan would debut in this chapter if next week is going to be a color page. Lancelot and Gowther got the same treatment after all. Curiously, Meliodas didn't, which could mean that it's going to happen later when we see him with a new outfit or something. Tristan's appearance is so far exactly what I expected. We can't see his full body, but I think he's going to be taller than his father and perhaps even taller than his mother. Will be interesting to see what happens with his squad in the future. Will Tristan have his own team to go on adventures with or will they all join Percival's group?
Isolde's magic seems like an inferior version of Guila's. Both can generate explosions, but Guila's doesn't require physical contact. I guess the ability to create landmines could also be useful, but it doesn't beat dropping bombs from the air. Jade's magic is weird. If blinding the enemy is the only thing it does then it's very basic, unless the black orb is unbreakable or something like that. Visually his magic is very similar to Melascula's black sphere that she used to trap people.
Chion's magic is the most interesting one of the bunch. He seems to basically be a Pokemon trainer who can command magical creatures that he keeps inside magic stones. The rocks remind me of the crystals that the druids used to store various monsters for training purposes, so maybe there's some kind of a connection there. Sylph is an air spirit, which means Chion probably also has control over the spirits of fire, water and earth, but he might possess other elementals or even mythical beasts like Cernunnos as well. Hell, maybe he could eventually tame an Indura to keep up with endgame powercreep.
Isolde might realyl be King and Diane's daughter with the way she was manipulating the ground.
It's not ground manipulation, it's explosions. When Percival used his magic to absorb hers, it turned the mini-Percival into a bomb. There was no contact with the ground there.