If you use /cells move 50 in an arena, the game freezes and crashes.

ERROR[Server]: In thread 7fd0e3fff640:
ERROR[Server]: /build/minetest/src/minetest-5.3.0/src/script/cpp_api/s_base.cpp:8c: static int ScriptApiBase::luaPanic(lua_State*): A fatal error occurred: LUA PANIC: unprotected error in call to Lua API (not enough memory)

When you're inside a node (cell or arena border), the screen turns black. This is not very useful for crowded arenas.

I suggest to make you see through the node when you're inside. Use post_effect_color for this. Don't forget you can set alpha in the ColorSpec.

Thank you for reading.

If you create an arena with /cells create, the arena's length, width and height are 1 node less than specified (each).

The icons for death, birth and both are hard to distinguish, the color is too close.

Although the player character is ca. 1 node high, you can't move through 1-node high gaps.

Suggestion: Maybe make the collision box a little bit smaller so you can "fit through".

Help window is small in width for text line and there is no horizontal scroll bar.
Tested on Minetest latest android version.

/cells resize crashes the game.

Try /cells resize 10.

You can place the cell on top of an arena, which removes the cell from your inventory.

You can't die, but you still experience the fall damage effect (red screen) when you hit the ground.

NOTE: The proper way to disable damage globally is to force-set enable_damage=false using minetest.settings:set_bool.