IndestructibleIndestructible is a static ability.
A permanent with indestructible can’t be destroyed. Such permanents aren’t destroyed by lethal damage, and they ignore the state-based action that checks for lethal damage (see rule 704.5g).
Multiple instances of indestructible on the same permanent are redundant. (CR 702.12)
Whenever Kotis deals combat damage to a player,
exileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) the top X cards of their library, where X is the amount of damage dealt. You may
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) any number of spells with mana value X or less from among them without paying their mana costs.