It's because you don't want to drain too much life and give your opponent an opening to mount a comeback
Masters of Evil Commander (1) Creature (30) Clockwork Droid Cyberman Patrol Cybermat The Master, Formed Anew Dalek Squadron The Cyber-Controller Vashta Nerada Weeping Angel Zygon Infiltrator Ashad, the Lone Cyberman Cult of Skaro Renegade Silent Solemn Simulacrum Sycorax Commander The Beast, Deathless Prince The Flood of Mars The Master, Gallifrey's End The Master, Mesmerist The Rani Vislor Turlough Dalek Drone Rassilon, the War President Sontaran General The Valeyard Time Reaper Auton Soldier Missy The Master, Multiplied Cybermen Squadron The Dalek Emperor Instant (4) Cyber Conversion Feed the Swarm Snuff Out This Is How It Ends Sorcery (8) Doomsday Confluence Delete Don't Blink Exterminate
In these, you can find five rare or mythic rares, as well as four uncommons and five commons, as well as one land
I'm no licensing expert by any stretch of the imagination, but I'd have to imagine there could still be issues based on that fact and the original card name alone
Bumbleflower is in play, target opponent draws a card, you put a +1/+1 counter on a creature you control, and that creature gains flying for the turn