Telepath Tactics remains almost entirely deterministic, moreso than pretty much any other tactics game in existence (except for its predecessors). The only real exceptions to this relentless determinism are random item drops, dodging, and status effects. I'll address each in turn.
Random item drops only occur in multiplayer games. These are important to discourage players from turtling, which otherwise leads to incredibly boring matches.
Dodging is there to add a little more tension to battles by making them a little bit more unpredictable; they don't add that much randomness, though. By default, dodging is something only two units can do, and there are specific tactics to counter it: using Mental attacks (which always hit) and using Shadow attacks (which impart Slowed status, reducing max movement range and preventing units from dodging attacks). Can dodging decide a really close match? Potentially, in rare instances; but there are tools for managing the risks involved, so I'm not concerned that it will cause random chance to trump player skill.
Status effect randomness is there because status effect attacks would be way too powerful if you could always count on them working. All you'd have to do is load up on cryokineticists and freeze the entire opposing army solid! Cryo Cross would basically be a guaranteed death sentence to the enemy. So you need a backup plan if you want to use a status effect attack; you just have to incorporate the risk of the attack not imparting the desired status effect into your planning.
